The Comprehensive Guide to JavaScript Design Patterns

The Comprehensive Guide to JavaScript Design Patterns

The Comprehensive Guide to JavaScript Design Patterns - As a good JavaScript developer, you strive to write clean, healthy, and maintainable code. You solve interesting challenges that, while unique, don’t necessarily require unique solutions.

Originally published by Marko Mišura at toptal.com

You’ve likely found yourself writing code that looks similar to the solution of an entirely different problem you’ve handled before. You may not know it, but you’ve used a JavaScript design pattern. Design patterns are reusable solutions to commonly occurring problems in software design.

During any language’s lifespan, many such reusable solutions are made and tested by a large number of developers from that language’s community. It is because of this combined experience of many developers that such solutions are so useful because they help us write code in an optimized way while at the same time solving the problem at hand.

The main benefits we get from design patterns are the following:

  • They are proven solutions: Because design patterns are often used by many developers, you can be certain that they work. And not only that, you can be certain that they were revised multiple times and optimizations were probably implemented.
  • They are easily reusable: Design patterns document a reusable solution which can be modified to solve multiple particular problems, as they are not tied to a specific problem.
  • They are expressive: Design patterns can explain a large solution quite elegantly.
  • They ease communication: When developers are familiar with design patterns, they can more easily communicate with one another about potential solutions to a given problem.
  • They prevent the need for refactoring code: If an application is written with design patterns in mind, it is often the case that you won’t need to refactor the code later on because applying the correct design pattern to a given problem is already an optimal solution.
  • They lower the size of the codebase: Because design patterns are usually elegant and optimal solutions, they usually require less code than other solutions.

I know you’re ready to jump in at this point, but before you learn all about design patterns, let’s review some JavaScript basics.

A Brief History of JavaScript

JavaScript is one of the most popular programming languages for web development today. It was initially made as a sort of a “glue” for various displayed HTML elements, known as a client-side scripting language, for one of the initial web browsers. Called Netscape Navigator, it could only display static HTML at the time. As you might assume, the idea of such a scripting language led to browser wars between the big players in the browser development industry back then, such as Netscape Communications (today Mozilla), Microsoft, and others.

Each of the big players wanted to push through their own implementation of this scripting language, so Netscape made JavaScript (actually, Brendan Eich did), Microsoft made JScript, and so forth. As you can image, the differences between these implementations were great, so development for web browsers was made per-browser, with best-viewed-on stickers that came with a web page. It soon became clear that we needed a standard, a cross-browser solution which would unify the development process and simplify the creation of web pages. What they came up with is called ECMAScript.

ECMAScript is a standardized scripting language specification which all modern browsers try to support, and there are multiple implementations (you could say dialects) of ECMAScript. The most popular one is the topic of this article, JavaScript. Since its initial release, ECMAScript has standardized a lot of important things, and for those more interested in the specifics, there is a detailed list of standardized items for each version of the ECMAScript available on Wikipedia. Browser support for ECMAScript versions 6 (ES6) and higher are still incomplete and have to be transpiled to ES5 in order to be fully supported.

What Is JavaScript?

In order to fully grasp the contents of this article, let’s make an introduction to some very important language characteristics that we need to be aware of before diving into JavaScript design patterns. If someone were to ask you “What is JavaScript?” you might answer somewhere in the lines of:

JavaScript is a lightweight, interpreted, object-oriented programming language with first-class functions most commonly known as a scripting language for web pages.

The aforementioned definition means to say that JavaScript code has a low memory footprint, is easy to implement, and easy to learn, with a syntax similar to popular languages such as C++ and Java. It is a scripting language, which means that its code is interpreted instead of compiled. It has support for procedural, object-oriented, and functional programming styles, which makes it very flexible for developers.

So far, we have taken a look at all of the characteristics which sound like many other languages out there, so let’s take a look at what is specific about JavaScript in regard to other languages. I am going to list a few characteristics and give my best shot at explaining why they deserve special attention.

JavaScript Supports First-class Functions

This characteristic used to be troublesome for me to grasp when I was just starting with JavaScript, as I came from a C/C++ background. JavaScript treats functions as first-class citizens, meaning you can pass functions as parameters to other functions just like you would any other variable.

// we send in the function as an argument to be
// executed from inside the calling function
function performOperation(a, b, cb) {
    var c = a + b;
    cb(c);
}

performOperation(2, 3, function(result) {
// prints out 5
console.log("The result of the operation is " + result);
})

JavaScript Is Prototype-based

As is the case with many other object-oriented languages, JavaScript supports objects, and one of the first terms that comes to mind when thinking about objects is classes and inheritance. This is where it gets a little tricky, as the language doesn’t support classes in its plain language form but rather uses something called prototype-based or instance-based inheritance.

It is just now, in ES6, that the formal term class is introduced, which means that the browsers still don’t support this (if you remember, as of writing, the last fully supported ECMAScript version is 5.1). It is important to note, however, that even though the term “class” is introduced into JavaScript, it still utilizes prototype-based inheritance under the hood.

Prototype-based programming is a style of object-oriented programming in which behavior reuse (known as inheritance) is performed via a process of reusing existing objects via delegations that serve as prototypes. We will dive into more detail with this once we get to the design patterns section of the article, as this characteristic is used in a lot of JavaScript design patterns.

JavaScript Event Loops

If you have experience working with JavaScript, you are surely familiar with the term callback function. For those not familiar with the term, a callback function is a function sent as a parameter (remember, JavaScript treats functions as first-class citizens) to another function and gets executed after an event fires. This is usually used for subscribing to events such as a mouse click or a keyboard button press.

Each time an event, which has a listener attached to it, fires (otherwise the event is lost), a message is being sent to a queue of messages which are being processed synchronously, in a FIFO manner (first-in-first-out). This is called the event loop.

Each of the messages on the queue has a function associated with it. Once a message is dequeued, the runtime executes the function completely before processing any other message. This is to say, if a function contains other function calls, they are all performed prior to processing a new message from the queue. This is called run-to-completion.

while (queue.waitForMessage()) {
queue.processNextMessage();
}

The queue.waitForMessage() synchronously waits for new messages. Each of the messages being processed has its own stack and is processed until the stack is empty. Once it finishes, a new message is processed from the queue, if there is one.

You might have also heard that JavaScript is non-blocking, meaning that when an asynchronous operation is being performed, the program is able to process other things, such as receiving user input, while waiting for the asynchronous operation to complete, not blocking the main execution thread. This is a very useful property of JavaScript and a whole article could be written just on this topic; however, it is outside of the scope of this article.

What Are Design Patterns?

As I said before, design patterns are reusable solutions to commonly occurring problems in software design. Let’s take a look at some of the categories of design patterns.

Proto-patterns

How does one create a pattern? Let’s say you recognized a commonly occurring problem, and you have your own unique solution to this problem, which isn’t globally recognized and documented. You use this solution every time you encounter this problem, and you think that it’s reusable and that the developer community could benefit from it.

Does it immediately become a pattern? Luckily, no. Oftentimes, one may have good code writing practices and simply mistake something that looks like a pattern for one when, in fact, it is not a pattern.

How can you know when what you think you recognize is actually a design pattern?

By getting other developers’ opinions about it, by knowing about the process of creating a pattern itself, and by making yourself well acquainted with existing patterns. There is a phase a pattern has to go through before it becomes a full-fledged pattern, and this is called a proto-pattern.

A proto-pattern is a pattern-to-be if it passes a certain period of testing by various developers and scenarios where the pattern proves to be useful and gives correct results. There is quite a large amount of work and documentation—most of which is outside the scope of this article—to be done in order to make a fully-fledged pattern recognized by the community.

Anti-patterns

As a design pattern represents good practice, an anti-pattern represents bad practice.

An example of an anti-pattern would be modifying the Object class prototype. Almost all objects in JavaScript inherit from Object (remember that JavaScript uses prototype-based inheritance) so imagine a scenario where you altered this prototype. Changes to the Object prototype would be seen in all of the objects that inherit from this prototype—which would be most JavaScript objects. This is a disaster waiting to happen.

Another example, similar to one mentioned above, is modifying objects that you don’t own. An example of this would be overriding a function from an object used in many scenarios throughout the application. If you are working with a large team, imagine the confusion this would cause; you’d quickly run into naming collisions, incompatible implementations, and maintenance nightmares.

Similar to how it is useful to know about all of the good practices and solutions, it is also very important to know about the bad ones too. This way, you can recognize them and avoid making the mistake up front.

Design Pattern Categorization

Design patterns can be categorized in multiple ways, but the most popular one is the following:

  • Creational design patterns
  • Structural design patterns
  • Behavioral design patterns
  • Concurrency design patterns
  • Architectural design patterns

Creational Design Patterns

These patterns deal with object creation mechanisms which optimize object creation compared to a basic approach. The basic form of object creation could result in design problems or in added complexity to the design. Creational design patterns solve this problem by somehow controlling object creation. Some of the popular design patterns in this category are:

  • Factory method
  • Abstract factory
  • Builder
  • Prototype
  • Singleton

Structural Design Patterns

These patterns deal with object relationships. They ensure that if one part of a system changes, the entire system doesn’t need to change along with it. The most popular patterns in this category are:

  • Adapter
  • Bridge
  • Composite
  • Decorator
  • Facade
  • Flyweight
  • Proxy

Behavioral Design Patterns

These types of patterns recognize, implement, and improve communication between disparate objects in a system. They help ensure that disparate parts of a system have synchronized information. Popular examples of these patterns are:

  • Chain of responsibility
  • Command
  • Iterator
  • Mediator
  • Memento
  • Observer
  • State
  • Strategy
  • Visitor

Concurrency Design Patterns

These types of design patterns deal with multi-threaded programming paradigms. Some of the popular ones are:

  • Active object
  • Nuclear reaction
  • Scheduler

Architectural Design Patterns

Design patterns which are used for architectural purposes. Some of the most famous ones are:

  • MVC (Model-View-Controller)
  • MVP (Model-View-Presenter)
  • MVVM (Model-View-ViewModel)

In the following section, we are going to take a closer look at some of the aforementioned design patterns with examples provided for better understanding.

Design Pattern Examples

Each of the design patterns represents a specific type of solution to a specific type of problem. There is no universal set of patterns that is always the best fit. We need to learn when a particular pattern will prove useful and whether it will provide actual value. Once we are familiar with the patterns and scenarios they are best suited for, we can easily determine whether or not a specific pattern is a good fit for a given problem.

Remember, applying the wrong pattern to a given problem could lead to undesirable effects such as unnecessary code complexity, unnecessary overhead on performance, or even the spawning of a new anti-pattern.

These are all important things to consider when thinking about applying a design pattern to our code. We are going to take a look at some of the design patterns I personally found useful and believe every senior JavaScript developer should be familiar with.

Constructor Pattern

When thinking about classical object-oriented languages, a constructor is a special function in a class which initializes an object with some set of default and/or sent-in values.

Common ways to create objects in JavaScript are the three following ways:

// either of the following ways can be used to create a new object
var instance = {};
// or
var instance = Object.create(Object.prototype);
// or
var instance = new Object();

After creating an object, there are four ways (since ES3) to add properties to these objects. They are the following:

// supported since ES3
// the dot notation
instance.key = "A key's value";

// the square brackets notation
instance["key"] = "A key's value";

// supported since ES5
// setting a single property using Object.defineProperty
Object.defineProperty(instance, "key", {
value: "A key's value",
writable: true,
enumerable: true,
configurable: true
});

// setting multiple properties using Object.defineProperties
Object.defineProperties(instance, {
"firstKey": {
value: "First key's value",
writable: true
},
"secondKey": {
value: "Second key's value",
writable: false
}
});

The most popular way to create objects is the curly brackets and, for adding properties, the dot notation or square brackets. Anyone with any experience with JavaScript has used them.

We mentioned earlier that JavaScript doesn’t support native classes, but it does support constructors through the use of a “new” keyword prefixed to a function call. This way, we can use the function as a constructor and initialize its properties the same way we would with a classic language constructor.

// we define a constructor for Person objects
function Person(name, age, isDeveloper) {
this.name = name;
this.age = age;
this.isDeveloper = isDeveloper || false;

this.writesCode = function() {
  console.log(this.isDeveloper? "This person does write code" : "This person does not write code");
}

}

// creates a Person instance with properties name: Bob, age: 38, isDeveloper: true and a method writesCode
var person1 = new Person("Bob", 38, true);
// creates a Person instance with properties name: Alice, age: 32, isDeveloper: false and a method writesCode
var person2 = new Person("Alice", 32);

// prints out: This person does write code
person1.writesCode();
// prints out: this person does not write code
person2.writesCode();

However, there is still room for improvement here. If you’ll remember, I mentioned previously that JavaScript uses prototype-based inheritance. The problem with the previous approach is that the method writesCode gets redefined for each of the instances of the Person constructor. We can avoid this by setting the method into the function prototype:

// we define a constructor for Person objects
function Person(name, age, isDeveloper) {
this.name = name;
this.age = age;
this.isDeveloper = isDeveloper || false;
}

// we extend the function's prototype
Person.prototype.writesCode = function() {
console.log(this.isDeveloper? "This person does write code" : "This person does not write code");
}

// creates a Person instance with properties name: Bob, age: 38, isDeveloper: true and a method writesCode
var person1 = new Person("Bob", 38, true);
// creates a Person instance with properties name: Alice, age: 32, isDeveloper: false and a method writesCode
var person2 = new Person("Alice", 32);

// prints out: This person does write code
person1.writesCode();
// prints out: this person does not write code
person2.writesCode();

Now, both instances of the Person constructor can access a shared instance of the writesCode() method.

Module Pattern

As far as peculiarities go, JavaScript never ceases to amaze. Another peculiar thing to JavaScript (at least as far as object-oriented languages go) is that JavaScript does not support access modifiers. In a classical OOP language, a user defines a class and determines access rights for its members. Since JavaScript in its plain form supports neither classes nor access modifiers, JavaScript developers figured out a way to mimic this behavior when needed.

Before we go into the module pattern specifics, let’s talk about the concept of closure. A closure is a function with access to the parent scope, even after the parent function has closed. They help us mimic the behavior of access modifiers through scoping. Let’s show this via an example:

// we  used an immediately invoked function expression
// to create a private variable, counter
var counterIncrementer = (function() {
var counter = 0;

return function() {
    return ++counter;
};

})();

// prints out 1
console.log(counterIncrementer());
// prints out 2
console.log(counterIncrementer());
// prints out 3
console.log(counterIncrementer());

As you can see, by using the IIFE, we have tied the counter variable to a function which was invoked and closed but can still be accessed by the child function that increments it. Since we cannot access the counter variable from outside of the function expression, we made it private through scoping manipulation.

Using the closures, we can create objects with private and public parts. These are called modules and are very useful whenever we want to hide certain parts of an object and only expose an interface to the user of the module. Let’s show this in an example:

// through the use of a closure we expose an object
// as a public API which manages the private objects array
var collection = (function() {
// private members
var objects = [];

// public members
return {
    addObject: function(object) {
        objects.push(object);
    },
    removeObject: function(object) {
        var index = objects.indexOf(object);
        if (index >= 0) {
            objects.splice(index, 1);
        }
    },
    getObjects: function() {
        return JSON.parse(JSON.stringify(objects));
    }
};

})();

collection.addObject("Bob");
collection.addObject("Alice");
collection.addObject("Franck");
// prints ["Bob", "Alice", "Franck"]
console.log(collection.getObjects());
collection.removeObject("Alice");
// prints ["Bob", "Franck"]
console.log(collection.getObjects());

The most useful thing that this pattern introduces is the clear separation of private and public parts of an object, which is a concept very similar to developers coming from a classical object-oriented background.

However, not everything is so perfect. When you wish to change the visibility of a member, you need to modify the code wherever you have used this member because of the different nature of accessing public and private parts. Also, methods added to the object after their creation cannot access the private members of the object.

Revealing Module Pattern

This pattern is an improvement made to the module pattern as illustrated above. The main difference is that we write the entire object logic in the private scope of the module and then simply expose the parts we want to be public by returning an anonymous object. We can also change the naming of private members when mapping private members to their corresponding public members.

// we write the entire object logic as private members and
// expose an anonymous object which maps members we wish to reveal
// to their corresponding public members
var namesCollection = (function() {
// private members
var objects = [];

function addObject(object) {
    objects.push(object);
}

function removeObject(object) {
    var index = objects.indexOf(object);
    if (index >= 0) {
        objects.splice(index, 1);
    }
}

function getObjects() {
    return JSON.parse(JSON.stringify(objects));
}

// public members
return {
    addName: addObject,
    removeName: removeObject,
    getNames: getObjects
};

})();

namesCollection.addName("Bob");
namesCollection.addName("Alice");
namesCollection.addName("Franck");
// prints ["Bob", "Alice", "Franck"]
console.log(namesCollection.getNames());
namesCollection.removeName("Alice");
// prints ["Bob", "Franck"]
console.log(namesCollection.getNames());

The revealing module pattern is one of at least three ways in which we can implement a module pattern. The differences between the revealing module pattern and the other variants of the module pattern are primarily in how public members are referenced. As a result, the revealing module pattern is much easier to use and modify; however, it may prove fragile in certain scenarios, like using RMP objects as prototypes in an inheritance chain. The problematic situations are the following:

  1. If we have a private function which is referring to a public function, we cannot override the public function, as the private function will continue to refer to the private implementation of the function, thus introducing a bug into our system.
  2. If we have a public member pointing to a private variable, and try to override the public member from outside the module, the other functions would still refer to the private value of the variable, introducing a bug into our system.

Singleton Pattern

The singleton pattern is used in scenarios when we need exactly one instance of a class. For example, we need to have an object which contains some configuration for something. In these cases, it is not necessary to create a new object whenever the configuration object is required somewhere in the system.

var singleton = (function() {
// private singleton value which gets initialized only once
var config;

function initializeConfiguration(values){
    this.randomNumber = Math.random();
    values = values || {};
    this.number = values.number || 5;
    this.size = values.size || 10;
}

// we export the centralized method for retrieving the singleton value
return {
    getConfig: function(values) {
        // we initialize the singleton value only once
        if (config === undefined) {
            config = new initializeConfiguration(values);
        }

        // and return the same config value wherever it is asked for
        return config;
    }
};

})();

var configObject = singleton.getConfig({ "size": 8 });
// prints number: 5, size: 8, randomNumber: someRandomDecimalValue
console.log(configObject);
var configObject1 = singleton.getConfig({ "number": 8 });
// prints number: 5, size: 8, randomNumber: same randomDecimalValue as in first config
console.log(configObject1);

As you can see in the example, the random number generated is always the same, as well as the config values sent in.

It is important to note that the access point for retrieving the singleton value needs to be only one and very well known. A downside to using this pattern is that it is rather difficult to test.

Observer Pattern

The observer pattern is a very useful tool when we have a scenario where we need to improve the communication between disparate parts of our system in an optimized way. It promotes loose coupling between objects.

There are various versions of this pattern, but in its most basic form, we have two main parts of the pattern. The first is a subject and the second is observers.

A subject handles all of the operations regarding a certain topic that the observers subscribe to. These operations subscribe an observer to a certain topic, unsubscribe an observer from a certain topic, and notify observers about a certain topic when an event is published.

However, there is a variation of this pattern called the publisher/subscriber pattern, which I am going to use as an example in this section. The main difference between a classical observer pattern and the publisher/subscriber pattern is that publisher/subscriber promotes even more loose coupling then the observer pattern does.

In the observer pattern, the subject holds the references to the subscribed observers and calls methods directly from the objects themselves whereas, in the publisher/subscriber pattern, we have channels, which serve as a communication bridge between a subscriber and a publisher. The publisher fires an event and simply executes the callback function sent for that event.

I am going to display a short example of the publisher/subscriber pattern, but for those interested, a classic observer pattern example can be easily found online.

var publisherSubscriber = {};

// we send in a container object which will handle the subscriptions and publishings
(function(container) {
// the id represents a unique subscription id to a topic
var id = 0;

// we subscribe to a specific topic by sending in
// a callback function to be executed on event firing
container.subscribe = function(topic, f) {
    if (!(topic in container)) {
      container[topic] = [];
    }

    container[topic].push({
        "id": ++id,
        "callback": f
    });

    return id;
}

// each subscription has its own unique ID, which we use
// to remove a subscriber from a certain topic
container.unsubscribe = function(topic, id) {
    var subscribers = [];
    for (var subscriber of container[topic]) {
        if (subscriber.id !== id) {
            subscribers.push(subscriber);
        }
    }
    container[topic] = subscribers;
}

container.publish = function(topic, data) {
    for (var subscriber of container[topic]) {
        // when executing a callback, it is usually helpful to read
        // the documentation to know which arguments will be
        // passed to our callbacks by the object firing the event
        subscriber.callback(data);
    }
}

})(publisherSubscriber);

var subscriptionID1 = publisherSubscriber.subscribe("mouseClicked", function(data) {
console.log("I am Bob's callback function for a mouse clicked event and this is my event data: " + JSON.stringify(data));
});

var subscriptionID2 = publisherSubscriber.subscribe("mouseHovered", function(data) {
console.log("I am Bob's callback function for a hovered mouse event and this is my event data: " + JSON.stringify(data));
});

var subscriptionID3 = publisherSubscriber.subscribe("mouseClicked", function(data) {
console.log("I am Alice's callback function for a mouse clicked event and this is my event data: " + JSON.stringify(data));
});

// NOTE: after publishing an event with its data, all of the
// subscribed callbacks will execute and will receive
// a data object from the object firing the event
// there are 3 console.logs executed
publisherSubscriber.publish("mouseClicked", {"data": "data1"});
publisherSubscriber.publish("mouseHovered", {"data": "data2"});

// we unsubscribe from an event by removing the subscription ID
publisherSubscriber.unsubscribe("mouseClicked", subscriptionID3);

// there are 2 console.logs executed
publisherSubscriber.publish("mouseClicked", {"data": "data1"});
publisherSubscriber.publish("mouseHovered", {"data": "data2"});

This design pattern is useful in situations when we need to perform multiple operations on a single event being fired. Imagine you have a scenario where we need to make multiple AJAX calls to a back-end service and then perform other AJAX calls depending on the result. You would have to nest the AJAX calls one within the other, possibly entering into a situation known as callback hell. Using the publisher/subscriber pattern is a much more elegant solution.

A downside to using this pattern is difficult testing of various parts of our system. There is no elegant way for us to know whether or not the subscribing parts of the system are behaving as expected.

Mediator Pattern

We will briefly cover a pattern which is also very useful when talking about decoupled systems. When we have a scenario where multiple parts of a system need to communicate and be coordinated, perhaps a good solution would be to introduce a mediator.

A mediator is an object which is used as a central point for communication between disparate parts of a system and handles the workflow between them. Now, it is important to stress out that it handles workflow. Why is this important?

Because there is a large similarity with the publisher/subscriber pattern. You might ask yourself, OK, so these two patterns both help implement better communication between objects… What is the difference?

The difference is that a mediator handles the workflow, whereas the publisher/subscriber uses something called a “fire and forget” type of communication. The publisher/subscriber is simply an event aggregator, meaning it simply takes care of firing the events and letting the correct subscribers know which events were fired. The event aggregator does not care what happens once an event was fired, which is not the case with a mediator.

A nice example of a mediator is a wizard type of interface. Let’s say you have a large registration process for a system you have worked on. Oftentimes, when a lot of information is required from a user, it is a good practice to break this down into multiple steps.

This way, the code will be a lot cleaner (easier to maintain) and the user isn’t overwhelmed by the amount of information which is requested just in order to finish the registration. A mediator is an object which would handle the registration steps, taking into account different possible workflows that might happen due to the fact that each user could potentially have a unique registration process.

The obvious benefit from this design pattern is improved communication between different parts of a system, which now all communicate through the mediator and cleaner codebase.

A downside would be that now we have introduced a single point of failure into our system, meaning if our mediator fails, the entire system could stop working.

Prototype Pattern

As we have already mentioned throughout the article, JavaScript does not support classes in its native form. Inheritance between objects is implemented using prototype-based programming.

It enables us to create objects which can serve as a prototype for other objects being created. The prototype object is used as a blueprint for each object the constructor creates.

As we have already talked about this in the previous sections, let’s show a simple example of how this pattern might be used.

var personPrototype = {
sayHi: function() {
console.log("Hello, my name is " + this.name + ", and I am " + this.age);
},
sayBye: function() {
console.log("Bye Bye!");
}
};

function Person(name, age) {
name = name || "John Doe";
age = age || 26;

function constructorFunction(name, age) {
    this.name = name;
    this.age = age;
};

constructorFunction.prototype = personPrototype;

var instance = new constructorFunction(name, age);
return instance;

}

var person1 = Person();
var person2 = Person("Bob", 38);

// prints out Hello, my name is John Doe, and I am 26
person1.sayHi();
// prints out Hello, my name is Bob, and I am 38
person2.sayHi();

Take notice how prototype inheritance makes a performance boost as well because both objects contain a reference to the functions which are implemented in the prototype itself, instead of in each of the objects.

Command Pattern

The command pattern is useful in cases when we want to decouple objects executing the commands from objects issuing the commands. For example, imagine a scenario where our application is using a large number of API service calls. Then, let’s say that the API services change. We would have to modify the code wherever the APIs that changed are called.

This would be a great place to implement an abstraction layer, which would separate the objects calling an API service from the objects which are telling them when to call the API service. This way, we avoid modification in all of the places where we have a need to call the service, but rather have to change only the objects which are making the call itself, which is only one place.

As with any other pattern, we have to know when exactly is there a real need for such a pattern. We need to be aware of the tradeoff we are making, as we are adding an additional abstraction layer over the API calls, which will reduce performance but potentially save a lot of time when we need to modify objects executing the commands.

// the object which knows how to execute the command
var invoker = {
add: function(x, y) {
return x + y;
},
subtract: function(x, y) {
return x - y;
}
}

// the object which is used as an abstraction layer when
// executing commands; it represents an interface
// toward the invoker object
var manager = {
execute: function(name, args) {
if (name in invoker) {
return invoker[name].apply(invoker, [].slice.call(arguments, 1));
}
return false;
}
}

// prints 8
console.log(manager.execute("add", 3, 5));
// prints 2
console.log(manager.execute("subtract", 5, 3));

Facade Pattern

The facade pattern is used when we want to create an abstraction layer between what is shown publicly and what is implemented behind the curtain. It is used when an easier or simpler interface to an underlying object is desired.

A great example of this pattern would be selectors from DOM manipulation libraries such as jQuery, Dojo, or D3. You might have noticed using these libraries that they have very powerful selector features; you can write in complex queries such as:

jQuery(".parent .child div.span")

It simplifies the selection features a lot, and even though it seems simple on the surface, there is an entire complex logic implemented under the hood in order for this to work.

We also need to be aware of the performance-simplicity tradeoff. It is desirable to avoid extra complexity if it isn’t beneficial enough. In the case of the aforementioned libraries, the tradeoff was worth it, as they are all very successful libraries.

Next Steps

Design patterns are a very useful tool which any senior JavaScript developer should be aware of. Knowing the specifics regarding design patterns could prove incredibly useful and save you a lot of time in any project’s lifecycle, especially the maintenance part. Modifying and maintaining systems written with the help of design patterns which are a good fit for the system’s needs could prove invaluable.

In order to keep the article relatively brief, we will not be displaying any more examples. For those interested, a great inspiration for this article came from the Gang of Four book Design Patterns: Elements of Reusable Object-Oriented Software and Addy Osmani’s Learning JavaScript Design Patterns. I highly recommend both books.


Originally published by Marko Mišura at toptal.com


===========================================

Thanks for reading :heart: If you liked this post, share it with all of your programming buddies! Follow me on Facebook | Twitter

Learn More

☞ Svelte.js - The Complete Guide

☞ The Complete JavaScript Course 2019: Build Real Projects!

☞ Become a JavaScript developer - Learn (React, Node,Angular)

☞ JavaScript: Understanding the Weird Parts

☞ JavaScript: Coding Challenges Bootcamp - 2019

☞ The Complete Node.js Developer Course (3rd Edition)

☞ Angular & NodeJS - The MEAN Stack Guide

☞ NodeJS - The Complete Guide (incl. MVC, REST APIs, GraphQL)

☞ Node.js Absolute Beginners Guide - Learn Node From Scratch

What is JavaScript – All You Need To Know About JavaScript

What is JavaScript – All You Need To Know About JavaScript

In this article on what is JavaScript, we will learn the basic concepts of JavaScript.

After decades of improvement, JavaScript has become one of the most popular programming languages of all time. It all started in the year 1995 when Brendan Eich created JavaScript in a span of 10 days. Since then, it has seen multiple versions, updates and has grown to the next level.

Here’s a list of topics that I’ll be covering in this blog:

  1. What is JavaScript
  2. What can JavaScript do?
  3. JavaScript Frameworks
  4. The Big Picture: HTML, CSS & JavaScript
  5. Benefits of JavaScript
  6. Fundamentals of JavaScript
    VariablesConstantsData TypesObjectsArraysFunctionsConditional statementsLoopsSwitch case
What is JavaScript?

JavaScript is a high level, interpreted, programming language used to make web pages more interactive.

Have you ever thought that your website is missing something? Maybe it’s not engaging enough or it’s not as creative as you want it to be. JavaScript is that missing piece which can be used to enhance web pages, applications, etc to provide a more user-friendly experience.

What is JavaScript?

JavaScript is the language of the web, it is used to make the web look alive by adding motion to it. To be more precise, it’s a programming language that let’s you implement complex and beautiful things/design on web pages. When you notice a web page doing more than just sit there and gawk at you, you can bet that the web page is using JavaScript.

Feature of JavaScript

Scripting language and not Java: In fact, JavaScript has nothing to do with Java. Then why is it called “Java” Script? When JavaScript was first released it was called Mocha, it was later renamed to LiveScript and then to JavaScript when Netscape (founded JavaScript) and Sun did a license agreement. Object-based scripting language which supports polymorphism, encapsulation and to some extent inheritance as well.**Interpreted language: **It doesn’t have to be compiled like Java and C which require a compiler.JavaScript runs in a browser: You can run it on Google Chrome, Internet Explorer, Safari, etc. JavaScript can execute not only in the browser but also on the server and any device which has a JavaScript Engine.

What is JavaScript – Stackoverflow stats

Currently, we have 100s of programming languages and every day new languages are being created. Among these are few powerful languages that bring about big changes in the market and JavaScript is one of them.

JavaScript has always been on the list of popular programming languages. According to StackOverflow, for the 6th year in a row, JavaScript has remained the most popular and commonly used programming language.

What can JavaScript do?

JavaScript is mainly known for creating beautiful web pages & applications. An example of this is Google Maps. If you want to explore a specific map, all you have to do is click and drag with the mouse. And what sort of language could do that? You guessed it! It’s JavaScript.JavaScript can also be used in smart watches. An example of this is the popular smartwatch maker called Pebble. Pebble has created Pebble.js which is a small JavaScript Framework that allows a developer to create an application for the Pebble line of watches in JavaScript.

What is JavaScript – Applications of JavaScript
Most popular websites like Google, Facebook, Netflix, Amazon, etc make use of JavaScript to build their websites.Among things like mobile applications, digital art, web servers and server applications, JavaScript is also used to make Games. A lot of developers are building small-scale games and apps using JavaScript.## JavaScript Frameworks

One major reason for the popularity of JavaScript is the JavaScript Frameworks. Here’s a brief introduction of the most trending JavaScript frameworks :

  1. AngularJS is Google’s web development framework which provides a set of modern development and design features for rapid application development.

  2. ReactJS is another top JavaScript framework mainly maintained by Facebook and it’s behind the User Interface of Facebook and Instagram, showing off its efficiency in maintaining such high traffic applications.

What is JavaScript – JavaScript Frameworks

  1. MeteorJS is mainly used for providing back-end development. Using JavaScript on the back-end to save time and build expertise is one of the major ideas behind Meteor.

  2. jQuery can be used when you want to extend your website and make it more interactive. Companies like Google, WordPress and IBM rely on jQuery.

The Big Picture: HTML, CSS & JavaScript

Anyone familiar with JavaScript knows that it has something to do with HTML and CSS. But what is the relationship between these three? Let me explain this with an analogy.

What is JavaScript – HTML, CSS and JavaScript

Think of HTML (HyperText Markup Language) as the skeleton of the web. It is used for displaying the web.

On the other hand, CSS is like our clothes. We put on fashionable clothes to look better. Similarly, the web is quite stylish as well. It uses CSS which stands for Cascading Style Sheets for styling purpose.

Then there is JavaScript which puts life into a web page. Just like how kids move around using the skateboard, the web also motions with the help of JavaScript.

Benefits of JavaScript

There has to be a reason why so many developers love working on JavaScript. Well, there are several benefits of using JavaScript for developing web applications, here’s a few benefits:

It’s easy to learn and simple to implement. It is a weak-type programming language unlike the strong-type programming languages like Java and C++, which have strict rules for coding.

It’s all about being fast in today’s world and since JavaScript is mainly a client-side programming language, it is very fast because any code can run immediately instead of having to contact the server and wait for an answer.

Rich set of frameworks like AngularJS, ReactJS are used to build web applications and perform different tasks.

**Builds interactive websites: **We all get attracted to beautifully designed websites and JavaScript is the reason behind such attractive websites and applications.

JavaScript is an interpreted language that does not require a compiler because the web interprets JavaScript. All you need is a browser like Google Chrome or Internet Explorer and you can do all sorts of stuff in the browser.

JavaScript is platform independent and it is supported by all major browsers like Internet Explorer, Google Chrome, Mozilla Firefox, Safari, etc.

JavaScript Fundamentals

In this What is JavaScript blog, we’ll cover the following basic fundamentals of JavaScript
VariablesConstantsData TypesObjectsArraysFunctionsConditional statementsLoopsSwitch case## Variables

Variable is a name given to a memory location which acts as a container for storing data temporarily. They are nothing but reserved memory locations to store values.

What is JavaScript – Variables

To declare a variable in JavaScript use the ‘let’ keyword. For example:

let age;
age=22;

In the above example, I’ve declared a variable ‘age’ by using the ‘let’ keyword and then I’ve stored a value (22) in it. So here a memory location is assigned to the ‘age’ variable and it contains a value i.e. ’22’.

Constants

Constants are fixed values that don’t change during execution time.

To declare a constant in JavaScript use the ‘const’ keyword. For example:

const mybirthday;
mybirthday='3rd August'; 

Data types

You can assign different types of values to a variable such as a number or a string. In JavaScript, there are two categories of data types :

What is JavaScript – Data Types

Objects

An object is a standalone entity with properties and types and it is a lot like an object in real life. For example, consider a girl, whose name is Emily, age is 22 and eye-color is brown. In this example the object is the girl and her name, age and eye-color are her properties.

What is JavaScript – Objects example

Objects are variables too, but they contain many values, so instead of declaring different variables for each property, you can declare an object which stores all these properties.

To declare an object in JavaScript use the ‘let’ keyword and make sure to use curly brackets in such a way that all property-value pairs are defined within the curly brackets. For example:

let girl= {
name: 'Emily',
age: 22,
eyeColour: 'Brown'
};

In the above example, I’ve declared an object called ‘girl’ and it has 3 properties (name, age, eye colour) with values (Emily, 22, Brown).

Arrays

An array is a data structure that contains a list of elements which store multiple values in a single variable.

For example, let’s consider a scenario where you went shopping to buy art supplies. The list of items you bought can be put into an array.

What is JavaScript – Arrays example

To declare an array in JavaScript use the ‘let’ keyword with square brackets and all the array elements must be enclosed within them. For example:

let shopping=[];
shopping=['paintBrush','sprayPaint','waterColours','canvas'];

In the above example I’ve declared an array called ‘shopping’ and I’ve added four elements in it.

Also, array elements are numbered from zero. For example this is how you access the first array element:

shopping[0];		

Functions

A function is a block of organised, reusable code that is used to perform single, related action.

Let’s create a function that calculates the product of two numbers.

To declare a function in JavaScript use the ‘function’ keyword. For example:

function product(a, b) {
return a*b;
}

In the above example, I’ve declared a function called ‘product’ and I’ve passed 2 parameters to this function, ‘a’ and ‘b’ which are variables whose product is returned by this function. Now, in order to call a function and pass a value to these parameters you’ll have to follow the below syntax:

product(8,2);

In the above code snippet I’m calling the product function with a set of values (8 & 2). These are values of the variables ‘a’ and ‘b’ and they’re called as arguments to the function.

Conditional statements – if

Conditional statement is a set of rules performed if a certain condition is met. The ‘if’ statement is used to execute a block of code, only if the condition specified holds true.

What is JavaScript – if flowchart

To declare an if statement in JavaScript use the ‘if’ keyword. The syntax is:

if(condition) {
statement;
}

Now let’s look at an example:

let numbers=[1,2,1,2,3,2,3,1];
if(numbers[0]==numbers[2]) {
console.log('Correct!');
}

In the above example I’ve defined an array of numbers and then I’ve defined an if block. Within this block is a condition and a statement. The condition is ‘(numbers[0]==numbers[2])’ and the statement is ‘console.log(‘Correct!’)’. If the condition is met, only then the statement will be executed.

Conditional statements- Else if

Else statement is used to execute a block of code if the same condition is false.

What is JavaScript – Else-if flowchart

The syntax is:

if(condition) {
statement a;
}
else (condition) {
statement b;
}

Now let’s look at an example:

let numbers=[1,2,1,2,3,2,3,1];
if(numbers[0]==numbers[4] {
console.log("Correct!");
}
else {
console.log("Wrong, please try again");
}

In the above example, I’ve defined an if block as well as an else block. So if the conditions within the if block holds false then the else block gets executed. Try this for yourself and see what you get!

**Loops **

Loops are used to repeat a specific block until some end condition is met. There are three categories of loops in JavaScript :

  1. while loop
  2. do while loop
  3. for loop
While loop

While the condition is true, the code within the loop is executed.

What is JavaScript – while loop flowchart

The syntax is:

while(condition) {
loop code;
}

Now let’s look at an example:

let i=0;
while(i < 5) {
console.log("The number is " +i);
i++;
}

In the above example, I’ve defined a while loop wherein I’ve set a condition. As long as the condition holds true, the while loop is executed. Try this for yourself and see what you get!

Do while loop

This loop will first execute the code, then check the condition and while the condition holds true, execute repeatedly.

What is JavaScript – Do while loop flowchart

Refer the syntax to better understand it:

do {
loop code;
} while(condition);

This loop executes the code block once before checking if the condition is true, then it will repeat the loop as long as the condition holds true.

Now let’s look at an example:

do {
console.log("The number is " +i);
i++;
}
while(i > 5);

The above code is similar to the while loop code except, the code block within the do loop is first executed and only then the condition within the while loop is checked. If the condition holds true then the do loop is executed again.

For loop

The for loop repeatedly executes the loop code while a given condition is TRUE. It tests the condition before executing the loop body.

What is JavaScript – for loop flowchart

The syntax is:

for(begin; condition; step) {
loop code;
}

In the above syntax:

  • begin statement is executed one time before the execution of the loop code
  • condition defines the condition for executing the loop code
  • step statement is executed every time after the code block has been executed

For example:

for (i=0;i<5;i++) {
console.log("The number is " +i);
}

In the above example, I’ve defined a for loop within which I’ve defined the begin, condition and step statements. The begin statement is that ‘i=0’. After executing the begin statement the code within the for loop is executed one time. Next, the condition is checked, if ‘i<5’ then, the code within the loop is executed. After this, the last step statement (i++) is executed. Try this and see what you get!

Switch Case

The switch statement is used to perform different actions based on different conditions.

What is JavaScript – Switch case flowchart

Let’s look at the syntax for switch case:

switch(expression) {
case 1:
code block 1
break;
case 2:
code block 2
break;
default:
code block 3
break;
}

How does it work?

  • Switch expression gets evaluated once
  • Value of the expression is compared with the values of each case
  • If there is a match, the associated block of code is executed

Let’s try this with an example:

let games='football';
switch(games) {
case "throwball":
console.log("I dislike throwball!");
break;
case "football":
console.log("I love football!");
break;
case "cricket":
console.log("I'm a huge cricket fan!");
break;
default:
console.log("I like other games");
break;
}

In the above example the switch expression is ‘games’ and the value of games is ‘football’. The value of ‘games’ is compared with the value of each case. In this example it is compared to ‘throwball’, ‘cricket’ and ‘football’. The value of ‘games’ matches with the case ‘football’, therefore the code within the ‘football’ case is executed. Try this for yourself and see what you get!

With this, we come to the end of this blog. I hope you found this blog informative and I hope you have a basic understanding of JavaScript. In my next blog on JavaScript I’ll be covering in-depth concepts, so stay tuned.

Also, check out our video on JavaScript Fundamentals if you want to get started as soon as possible and don’t forget to leave a comment if you have any doubt and also, let us know whether you’d want us to create more content on JavaScript. We are listening!

Learn JavaScript in 60 Minutes | JavaScript Crash Course | JavaScript Tutorial |

This video on "JavaScript" will help you learn JavaScript basics and fundamental concepts in 60 minutes. This will provide you in-depth knowledge about the JavaScript fundamentals that will help you write your own code in JavaScript and build a website. This JavaScript tutorial covers following topics..

==================================

Thanks for reading :heart: If you liked this post, share it with all of your programming buddies! Follow me on Facebook | Twitter

Learn More

Svelte.js - The Complete Guide

The Complete JavaScript Course 2019: Build Real Projects!

Advanced CSS and Sass: Flexbox, Grid, Animations and More!

CSS - The Complete Guide (incl. Flexbox, Grid & Sass)

CSS Bootcamp - Master CSS (Including CSS Grid / Flexbox)

Build Responsive Real World Websites with HTML5 and CSS3

Become a JavaScript developer - Learn (React, Node,Angular)

JavaScript: Understanding the Weird Parts

Vue JS 2 - The Complete Guide (incl. Vue Router & Vuex)

The Full JavaScript & ES6 Tutorial - (including ES7 & React)

JavaScript - Step By Step Guide For Beginners

JavaScript | How to use classes in JavaScript

JavaScript | How to use classes in JavaScript

Classes in JavaScript are a special syntax for its prototypical inheritance model that resembles class based inheritance in other object oriented languages. Classes are just special functions that can be declared to resembles classes in other languages. In JavaScript, we can have class declarations and class expressions, because they are just functions. So like all other functions, there are function declarations and function expressions. Classes serve a templates to create new objects.

Defining Classes

To declare a class, or make a class declaration, we use the class keyword to do so. For example, to declare a simple class, we can write:

class Person{
  constructor(firstName, lastName) {
    this.firstName= firstName;
    this.lastName = lastName;
  }
}

Class declarations aren’t hoisted so they can used before they are defined in the code, as the JavaScript interpreter will not automatically pull them up to the top. So the class above won’t work before it’s defined in the code like the following:

const person = new Person('John', 'Smith');
class Person{
  constructor(firstName, lastName) {
    this.firstName = firstName;
    this.lastName = lastName;
  }
}

We will get a ReferenceError if we run the code above.

We can also define a class by a class expression, which is an alternative syntax for defining a class. They can be named or unnamed. We can also assign a class to a variable like we do with functions. If we do that, we can reference the class by its name. For example, we can define:

let Person = class {
  constructor(firstName, lastName) {
    this.firstName = firstName;
    this.lastName = lastName;
  }
}

To get the name of the unnamed classes above, we can get the name with the name property, like so:

console.log(Person.name);


We can also undefined a named class like the following:


let Person = class Person2{
  constructor(firstName, lastName) {
    this.firstName = firstName;
    this.lastName = lastName;
  }
}

Then to get the name of the class, we can use the name property again. So we if we write:

console.log(Person.name)


we get Person2 logged.

The class body is defined with curly brackets. We define the class members inside the brackets. The body of the class is executed in strict mode, so everything defined in strict mode applies to the definition of a class, so we can’t define variables with out some keyword before it like var , let or const , and many other rules apply when you define a class. Classes in JavaScript also have a constructor method that lets us set fields when the object is instantiated with a class . Each class can only have one constructor method in it. If there’s more than one, then SyntaxError will be thrown. A constructor have to also call the super method to call the constructor of the super class inside if it the class extends a parent class.

Methods that aren’t declared static constitutes of the prototypical methods of the class. They are called after an object has been created by using the new keyword. For example, the following class have only prototypical methods:


class Person{
  constructor(firstName, lastName) {
    this.firstName = firstName;
    this.lastName = lastName;
  }
  get fullName(){
    return `${this.firstName} ${this.lastName}`  
  }
  sayHi(){
    return `Hi, ${this.firstName} ${this.lastName}`
  }
}

In the Person class above, fullName and sayHi are prototypical methods. They are called like this:

const person = new Person('Jane', 'Smith');
person.fullName() // 'Jane Smith'

Static methods are methods that can be called without creating an object from the class using the new keyword. For instance, we can have something like the following:


class Person {
  constructor(firstName, lastName) {
    this.firstName = firstName;
    this.lastName = lastName;
  }
  get fullName() {
    return `${this.firstName} ${this.lastName}`
  }
  sayHi() {
    return `Hi, ${this.firstName} ${this.lastName}`
  }
  static personCount() {
    return 3;
  }
}

We can call the personCount function without using the new keyword to create an instance of the class. So if we write:

Person.personCount

We get 3 returned.

The this value inside prototypical methods will be the value of the object. For static methods the value of this has the class that the static method is in as the value.

Getters and Setters

JavaScript classes can have getters and setter functions. Getters, as the name suggests, is a method that lets us get some data from a class. Setters are methods that gives us the ability to set some fields of the class. We denote getter functions with the get keyword and setters with the set keyword. For example, we can write a class that has getters and setters like the following:

class Person {
  constructor(firstName, lastName) {
    this._firstName = firstName;
    this._lastName = lastName;
  }
  get fullName() {
    return `${this.firstName} ${this.lastName}`
  }
  get firstName() {
    return this._firstName
  }
  get lastName() {
    return this._lastName
  }
  sayHi() {
    return `Hi, ${this.firstName} ${this.lastName}`
  }
  set firstName(firstName) {
    this._firstName = firstName;
  }
  set lastName(lastName) {
    this._lastName = lastName;
  }
}

Then when we use the new keyword to construct a Person object, we can use them in the following way:


const person = new Person('Jane', 'Smith');
person.firstName = 'John';
person.lastName = 'Doe';
console.log(person.firstName, person.lastName)

Since we have the getter and setter functions, we can use them to set the data directly to set the data for firstName and lastName of the Person class. In the setter functions, which start with the keyword set , what we assign to them get passed into the parameters and set in the member of the class. In the getter functions, which are denote by get we return the member values so that we can use them.

JavaScript Inheritance

In JavaScript, we can create classes where the properties can be included in the properties of a child class.

So, we can have a high-level class that contains the properties that are common to all the child classes, and the child class can have its own special properties that are not in any other classes.

For example, if we have an Animal class with the common properties and methods, like name and the eat method, then the Bird class can just inherit the common properties in the Animal class. They don’t have to be defined in the Bird class again.

We can write the following to do inheritance in JavaScript:

class Animal {
  constructor(name) {
    this.name = name;
  }
  eat() {
    console.log('eat');
  }
}
class Bird extends Animal {
  constructor(name, numWings) {
    super(name);
    this.numWings = numWings;
  }
}
const bird = new Bird('Joe', 2);
console.log(bird.name)
bird.eat();

In the example above, we have the parent class, Animal, that has the eat method, which all classes that extends from Animal will have, so they don’t have to define eat again.

We have the Bird class which extends the Animal class. Note that in the constructor of the Bird class, we have the super() function call to call the parent’s class constructor to populate the properties of the parent class in addition to the properties of the child class.

Classes cannot extend regular objects, which cannot be constructed with the new keyword. If we want to inherit from a regular object, we have to use the Object.setPrototypeOf function to set a class to inherit from a regular object. For example:

const Animal = {
  eat() {
    console.log(`${this.name} eats`);
  }
};
class Cat{
  constructor(name) {
    this.name = name;
  }
}
class Chicken{
  constructor(name) {
    this.name = name;
  }
}
Object.setPrototypeOf(Cat.prototype, Animal);
Object.setPrototypeOf(Chicken.prototype, Animal);
let cat = new Cat('Bob');
let chicken = new Chicken('Joe');
cat.eat();
chicken.eat();

If we run the example code above, we have see Bob eats and Joe eats logged because we have inherited the eat function from the Animal object.

this Keyword

The this keyword allows us to access the current object’s properties inside an object, unless you’re using arrow functions.

As we can see from the above example, we can get the properties of the instance of the child and the parent class in the object.

Mixins

We can use mixins to do multiple inheritance in JavaScript. Mixins are templates for creating classes. We need mixins to do multiple inheritance because JavaScript classes can only inherit from one super class, so multiple inheritance isn’t possible.

For example, if we have a base class, we can define mixins to incorporate the members from multiple classes into one by composing the mixins by calling one and then pass the returned result into the next one as the argument, an so on, like so:

class Base {
  baseFn() {
    console.log('baseFn called');
  }
}
let classAMixin = Base => class extends Base {
  a() {
    console.log('classAMixin called');
  }
};
let classBMixin = Base => class extends Base {
  b() {
    console.log('classBMixin called');
  }
};
class Bar extends classAMixin(classBMixin(Base)) {}
const bar = new Bar();
bar.baseFn()
bar.a()
bar.b()

In the code above, we have the Base class which we pass into the classBMixin to get the b function into the Base class, then we call the classAMixin by passing in the result of classBMixin(Base) into the argument of the classAMixin to return the a function from classAMixin into the Base class and then return the whole class with all the functions from all the classes incorporated into one.

If we call all the functions above like we did by creating an instance of the Bar object and then call the baseFn , a and b functions, then we get:

baseFn called
classAMixin called
classBMixin called

This means that we have all the functions from the mixins incorporated into the new Bar class.

In JavaScript, classes are just syntactic sugar to make the prototypical inheritance of JavaScript clearer by letting us structure the code in a way that’s more like typical inheritance class based object oriented inheritance pattern. This means that we write classes to and use the new keyword to create objects from the classes, but underneath the syntactic sugar, we are still using prototypical inheritance to extend objects. We can extend classes from objects and we can also use mixins to do multiple inheritance in of JavaScript classes.