Introduction to JavaScript Property Getters and Setters

Property getters and setters allow you to change the default behavior when accessing or modifying object properties. This tutorial teach you all you need to know about them. You will learn what JavaScript property getters and setters are, how they work and how to use them.

Properties and property getters and setters

In JavaScript, there are two types of properties. The first type is data properties. These are the properties you usually use when you work with objects. The second type is called “accessor properties”. These are a bit different. Put simply, accessor properties are methods.

These methods are executed every time you work with a property. When you access, or get, a value or when you set or change a value. What about property getters and setters? These two represent this group of properties, the accessor properties. To be more specific, getter is that function that is executed when you access some value.

Setter, on the other hand, is that function that is executed when you set or change a value. Interesting thing is that these methods are executed automatically. Well, this assumes there is some existing getter or setter. You don’t have to call them explicitly. You don’t have to call them at all.

All that is needed is someone trying to access and set a value of some property. If there is a getter or setter for that specific property it will be executed. Now, let’s take a look at each.

Property getters

Property getters, or methods, are used to access properties of objects. When you want to get value of some property, and this property has a getter method, that method will be executed. The getter method looks like a regular object method. The difference is the get keyword.

This get keyword is what tells JavaScript that you don’t want to create regular object method, but a getter method. The way to use this keyword is to put it as first, before the name of the getter method. What follows is the name of the getter, parentheses and function body.

// Syntax
// Create an object
const myObj = {
  // Example of a getter method
  // this getter will be executed
  // when you use myObj.myGetter
  get myGetter() {
    // Return something
    return ''
  }
}

// Execute the getter method
// NOTE: when you use getter method
// don't use parentheses at the end
myObj.myGetter

// Example:
// Create an object
const dog = {
  name: 'Jack',

  // Create getter method
  // this getter will be executed
  // when you use dog.getName
  get getName() {
    // this here refers to the "dog" object
    return `My dog's name is: ${this.name}`
  }
}

// Execute the getter method
console.log(dog.getName)
// Output:
// "My dog's name is: Jack"

One thing to remember. Property getter should always return something, some value. If it doesn’t return anything, you will get undefined when you try to use the getter. So, if you do add getter method, make sure it also contains return statement and returns something.

// Create an object
const dog = {
  name: 'Jack',

  get getName() {}
}

// Execute the getter method "getName"
console.log(dog.getName)
// Output:
// undefined

Property setters

When you set or change value of some property JavaScript will execute existing property setter, or setter method, for that property. The syntax of setter method is almost the same as of getter. One thing that is different is the keyword. When you want to define a setter you have to use set keyword, instead of get.

This keyword tells JavaScript that the method that follows is a setter method. Another thing that is different is that you will probably want to specify at least one parameter. The setter method is used to set value. Method parameter is a way to pass that value to a setter so it can be used.

Lastly, unlike, the getter method, the setter method doesn’t have to return anything. Setter is used to set values and no one probably expects it to return anything. So, omitting return statement is perfectly fine.

// Syntax
// Create an object
const myObj = {
  // Example of a setter method
  // this setter will be executed
  // when you use myObj.mySetter = ...
  get mySetter() {
    // Return something
    return ''
  }
}

// Execute the setter method "mySetter"
// NOTE: when you use setter method
// you use as if you were assigning a value
myObj.mySetter = 'Hello'

// Example:
// Create an object
const user = {
  name: 'Stuart Douglass',
  isAdmin: false,

  // Create setter method
  // this setter will be executed
  // when you use user.setName = ...
  set setName(newName) {
    // Allow only string with more than 0 characters
    if (typeof newName === 'string' && newName.length > 0) {
      this.name = newName
    } else {
      if (typeof newName !== 'string') {
        console.log('Please use only string.')
      } else if (newName.length === 0) {
        console.log('Please use name with more than 0 characters.')
      }
    }
  }
}

// Try to change the value of "name" to an empty string
// This executes the setter method for "name"
user.setName = ''
// 'Please use name with more than 0 characters.'

// Try to change the value of "name" to a number
// This executes the setter method for "name"
user.setName = 55
// 'Please use only string.'

// Check the value of "name" property
// This executes the getter method for "name"
console.log(user.name)
// Output:
// 'Stuart Douglass'

// Try to change the value of "name" to a string
// This executes the setter method for "name"
user.setName = 'Jeremy Guire'

// Check the value of "name" property again
// This executes the getter method for "name"
console.log(user.name)
// Output:
// 'Jeremy Guire'

Getters and setters as property wrappers

As you saw on previous examples, you can use getters and setters to restrict changes to property values. For example, you can reject change of a string value if new value is not a string. Or, you can reject the change if the new string is empty. You saw this in the previous with setName setter method.

In this example, there is an if…else statement that checks the new value before it lets it override the old value. This is one potential use case for getter and setter methods. You can use these methods to dynamically check values before someone can access them and/or change them.

One problem is that you can’t create getter or setter with the same name as existing property. This unfortunately doesn’t work. However, you do something different. You can change the name of those original properties to maybe less user-friendly. Then, you can use user-friendly names for getter and setter methods.

In programming, there is a well-known convention to start property name with an underscore (_) to mark it as internal. Internal means that no one should use it directly from the outside the object. You can use this convention with properties for which you want to add getters and setters.

So, here is what to do. First, prefix all properties that will have getter and setter methods with underscore. Second, create property getters and setters with the same names, but now without the underscore prefix. This will give you properties with friendly names that you have more control over.

const car = {
  // Add properties, prefixed with '_'
  _manufacturer: 'BWM',
  _model: 'i8',
  _year: '2020',

  // Create getter method for "_manufacturer"
  get manufacturer() {
    return this._manufacturer
  },

  // Create setter method for "_manufacturer"
  set manufacturer(newManufacturer) {
    if (typeof newManufacturer === 'string' && newManufacturer.length > 0) {
      this._manufacturer = newManufacturer
    }
  },

  // Create getter method for "_model"
  get model() {
    return this._model
  },

  // Create setter method for "_model"
  set model(newModel) {
    if (typeof newModel === 'string' && newModel.length > 0) {
      this._model = newModel
    }
  },

  // Create getter method for "_year"
  get year() {
    return this._year
  },

  // Create setter method for "_year"
  set year(newYear) {
    if (typeof newYear === 'string' && newYear.length > 0) {
      this._year = newYear
    }
  }
}

// Get current manufacturer
// Execute getter methods
console.log(car.manufacturer)
// Output:
// 'BWM'

// Get current model
console.log(car.model)
// Output:
// 'i8'

// Get current year
console.log(car.year)
// Output:
// '2020'

// Change some values
// Execute setter methods
car.manufacturer = 'Tesla'
car.model = 'Model S'

// Get new manufacturer
// Execute getter methods
console.log(car.manufacturer)
// Output:
// 'Tesla'

// Get new model
console.log(car.model)
// Output:
// 'Model S'

#javascript #programming #web-development #developer

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Introduction to JavaScript Property Getters and Setters
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What's New in ECMAScript 2022 (ES2022/ES13)?

Howdy, folks! The fact that you're here means you're looking for the new JavaScript features you can use in the close future. But by any chance, if you're not familiar with TC39, ECMA, or ECMAScript, check this article before reading this one, because you will need to know these to understand some of the following parts.

The transparent stages of the TC39

TC39 is an amazing and dedicated group of people who come from many different backgrounds and have one goal in common: they want to help to make the JavaScript language better. To do so, they have to keep many things in mind, and one rule they have is "don't break the web". Their approach to the language actually reminds me of the medical approach to the patients: "First, do no harm". Every step is carefully and meticulously calculated, so they don't break the existing parts.

Every feature that gets added to the spec has to go through the following 5 stages, just like drug trials. To proceed to the next stage, each has to achieve certain criteria. To be added to the ECMAScript spec, a feature has to be at least on stage 4.

  • Stage 0 / Proposal: A new possible feature that is planned to be presented to the committee, or proposals that haven't yet achieved the criteria to pass to the next stage. Check out the current stage 0 proposals from here.
  • Stage 1 / Proposal: Still primitive, but the committee is willing to spend time on solving this problem and the general structure of the API is defined. Check out the current stage 1 proposals from here.
  • Stage 2 / Draft: Critical aspects of the proposal and its problems are solved. These features are expected to exist in future versions of the spec. Check out the current stage 2 proposals from here.
  • Stage 3 / Candidate: The proposal is comprehensively and meticulously reviewed, no stone is left unturned. This is the final stage before the feature actually makes it to the spec. Check out the current stage 3 proposals from here.
  • Stage 4 / Finished: Congrats, you are in the spec! Check out the finished proposals from here.

The ones who made it before

JavaScript is an evolving language, and some features we use today were actually added pretty recently. After 2015, TC39 decided to make the changes annually, so each year they decide which new features are ready to be added. This is the list of the features that have been added to the spec after 2015:

ES2016

  • Array.prototype.includes(): Determines if a given element is included in the specified array. String.prototype.contains() was also deprecated and String.prototype.includes() was added to determine if a given string in included in another string.
  • Exponentiation operator(** and **=): a**b is shorthand notation for Math.pow(a,b), and a **= b is shorthand for a = a**b

ES2017

  • Object.values / Object.entries: Retrieves an array of values / arrays of key-value pairs, respectively.
  • Trailing commas in function parameter lists and calls: Both (a) => {} and (a,) => {} are valid function definitions, and both foo(a) and foo(a,) are valid function calls.
  • Async functions: async/await was introduced to JavaScript
  • Object.getOwnPropertyDescriptors(): Returns the property descriptors of all own properties of an object.
  • String.prototype.padStart() / String.prototype.padEnd(): Takes two arguments, first one being the repeat number, second one being the string that is going to be added and adds padding to the start or end of a given string.

ES2018

  • Promise.prototype.finally: Finally was introduced to register a callback function that runs when a promise is settled (either fulfilled or rejected)
  • Rest and spread operators(...): Rest operator collects values in an array. The spread operator spreads the values in an iterator.
  • Asynchronous iteration: for-await-of was introduced. It is a variation of the for-of iteration statement and can be used in async iterable objects.
  • Improvements on Regular Expressions: RegExp Unicode Property Escapes, RegExp Lookbehind Assertions, s(dotAll) flag for regular expressions, RegExp named capture groups

ES2019

  • Array.prototype.flat(): Flattens nested arrays up to a provided depth. Default depth is 1.
  • Array.prototype.flatMap(): Flattens and maps a given array subsequently. Flattening depth is 1.
  • Object.fromEntries(): Builds an object from given key-value pairs.
  • String.prototype.trimStart(): Trims the start of a given string.
  • String.prototype.trimEnd(): Trims the end of a given string.
  • Symbol.prototype.description: Read-only and optional string description for the Symbol objects.
  • Optional catch binding: Allows the omission of the catch block.
  • Also the implementation of some existing features have changed, such as JSON.stringify(), Function.prototype.toString() and Array.sort()

ES2020

  • String.prototype.matchAll(): Returns all matches for a global regex.
  • dynamic imports: Before this, we could only use static imports, which only accepted strings for the module path. With dynamic imports, we got to conditionally import modules by using promises.
  • BigInt: A new primitive data type that represents numbers bigger than 2⁵³.
  • Promise.allSettled(): Returns when all given promises are settled (rejected or fulfilled, doesn't matter).
  • globalThis: Before this, the global object had different syntax in different JavaScript environments (in a web browser it can be either window, self, frames, or this, in web workers it is self, in Node.js it is global). globalThis provided a single syntax for the global object in all JavaScript environments.
  • Optional Chaining Operator(?.): Legible property chains that don't throw an error if a requested reference is missing. If one of the chained properties is nullish (null or undefined), the whole expression returns undefined.
  • Nullish coalescing operator(??): Binary operator. If the value of the left side expression is null or undefined, the right side of the operator is evaluated.

ES2021

  • String.prototype.replaceAll(): Replaces all the occurrences of a given string with another.
  • Promise.any(): resolves if any of the given promises are resolved.
  • Underscore as a numeric separator: To increase legibility in bigger numbers, numeric separators can be replaced with underscores.
  • Logical assignment operators(&&=, ||=, ??=) All of them are binary operators, with the added functionality for assignment. For &&=, if the left side is truthy, the right-side expression is evaluated and assigned to the variable on the left side. For ||= if the left side is falsy, the right-side expression is evaluated and assigned to the left-side variable. With the ??=, if the left-side value is null or undefined, the right-side expression is evaluated and assigned to the variable on the left side.
  • WeakRefs and Finalizers: This is a class that helps you create weak references to objects, so they can be garbage collected. A FinalizationRegistry object lets you register a callback that will allow you to invoke when the object is garbage collected.

The ones who made it to ES2022

Alright! You can check the latest spec that was published from here.

1. Class Fields:

Class Public Instance Fields & Private Instance Fields:

Since ES2015, we could define fields by simply setting them up in our constructors. As a convention, fields that were not supposed to be accessed outside of the class methods were preceded by an underscore, but this did not stop any consumer of this class from accessing them anyway.

class ColorButton extends HTMLElement {
  
  constructor() {
    this.color = "red"
    this._clicked = false
  }
}

const button = new ColorButton()
// Public fields can be accessed and changed by anyone
button.color = "blue" 

// Curse your sudden but inevitable betrayal 
console.log(button._clicked) // Prints: false, can be accessed from the instance
button._clicked = true // Doesn't throw an error, can be read from the instance

The first part of this proposal offers a more clear way to define the fields in a class. Instead of defining them in our constructor, we can now define, and if we want to, initialize them on the top level of our classes.

class ColorButton extends HTMLElement {
  color = "red"
  _clicked = false
}

The second part offers a more secure way of hiding private fields from prying eyes. Instead of the conventional underscore, we can now use a preceding # in the field names to block anybody from accessing them outside of the class they're defined on.

class ColorButton extends HTMLElement {
  // All fields are public by default
  color = "red"

  // Private fields start with a #, can only be changed from inside the class
  #clicked = false
}

const button = new ColorButton()
// Public fields can be accessed and changed by anyone
button.color = "blue"

// SyntaxError here 
console.log(button.#clicked) // Cannot be read from outside
button.#clicked = true // Cannot be assigned a value from outside

Private instance methods and accessors:

Some methods and variables of a class are internally important for that class to behave like it's supposed to, but shouldn't be accidentally reached from outside. To protect these implementation details and keep them strictly internal, we can use private methods and accessors with the syntax of a preceding #.

class Banner extends HTMLElement {
  // Private variable that cannot be reached directly from outside, but can be modified by the methods inside:

  #slogan = "Hello there!"
  #counter = 0

  // private getters and setters (accessors):

  get #slogan() {return #slogan.toUpperCase()}
  set #slogan(text) {this.#slogan = text.trim()}

  get #counter() {return #counter}
  set #counter(value) {this.#counter = value}

  constructor() {
    super();
    this.onmouseover = this.#mouseover.bind(this);
  }

  // private method:
  #mouseover() {
    this.#counter = this.#counter++;
    this.#slogan = `Hello there! You've been here ${this.#counter} times.`
  }
}

Static class fields and private static methods:

Static class fields and methods are useful when you want certain fields and methods to only exist in the prototype, but not in every instance of the given class. On the other side, you might also want to allow some of these fields and methods to be only accessed from within the class.

Since ES2015, we can define static fields on a class by simply defining the field on the class itself.

class Circle {}
Circle.PI = 3.14

Going forward, we are now able to define these static fields inside the class definition using the static keyword.

class Circle {
  static PI = 3.14
}

Just like we did with class fields and methods, we can use the # prefix to set any static method or field as private. This prevents access to these static fields and methods from the outside, meaning they can only be accessed from inside the class.

class Circle {
  static #PI = 3.14

  static #calculateArea(radius) {
    return #PI * radius * radius
  }

  static calculateProperties(radius) {
    return {
      radius: radius,
      area: #calculateArea(radius)
    }
  }

}

// Public static method, outputs {radius: 10, area: 314}
console.log(Circle.calculateProperties(10))

// SyntaxError - Private static field
console.log(Circle.PI)

// SyntaxError - Private static method
console.log(Circle.calculateArea(5))

2. Ergonomic brand checks for Private Fields:

In public fields, if you try to access a non-existent field on a class, you get undefined as a result. However, private class fields throw an exception instead of returning undefined when you try to access a non-existent field on an object. Then, one way to check if a private field exists in an object is to see if accessing that field inside the class throws an exception or not. However, this approach has a big shortcoming. The exception might simply be because of another reason, such as a faulty getter on an existing field.

That's why, in keyword was proposed to allow us to check if a given private property/method exists in a class instance:

class VeryPrivate {
  constructor() {
    super()
  }

  #variable
  #method() {}
  get #getter() {}
  set #setter(text) {
    this.#variable = text
  }

  static isPrivate(obj) {
    return (
      #variable in obj && #method in obj && #getter in obj && #setter in obj
    )
  }
}

3. RegExp Match Indices

Regular expressions allow us to search for patterns in strings. If you're not familiar with regular expressions, you might want to start by reading this article first.

Both Regexp.exec and String.matchAll gives us a list of matches as a result. Regexp.exec gives these results one by one, so you need to call it multiple times to get all matches until it returns null. On the other hand String.matchAll returns an iterator where you can iterate over all matches. These results include both the full string of characters and the parenthesized substrings being matched, the input string and the 0-based index of the match. Take a look at the following example:


const str = 'Ingredients: cocoa powder, cocoa butter, other stuff'
const regex = /(cocoa) ([a-z]+)/g
const matches = [...str.matchAll(regex)]

// 0: "cocoa powder", 1: "cocoa", 2: "powder"
// index: 13
// input: "Ingredients: cocoa powder, cocoa butter, other stuff"
console.log(matches[0])


// 0: "cocoa butter", 1: "cocoa", 2: "butter"
// index: 27
// input: "Ingredients: cocoa powder, cocoa butter, other stuff"
console.log(matches[1])

While these results are pretty informative about the location of the entire match in the original input, they lack information regarding the indices of the substring matches. By using the new /d flag, we can ask for the start and end positions of each matched capture group.


const str = 'Ingredients: cocoa powder, cocoa butter, other stuff'
const regex = /(cocoa) ([a-z]+)/gd
const matches = [...str.matchAll(regex)]

// 0: "cocoa powder", 1: "cocoa", 2: "powder"
// index: 13
// input: "Ingredients: cocoa powder, cocoa butter, other stuff"
// indices: [[13,25],[13,18],[19,25]]
console.log(matches[0])


// 0: "cocoa butter", 1: "cocoa", 2: "butter"
// index: 27
// input: "Ingredients: cocoa powder, cocoa butter, other stuff"
// indices: [[27,39],[27,32],[33,39]]
console.log(matches[1])

4. Top-level await:

Until this point, we could only use await in the scope of async functions. This was fine until it wasn't, like when we hit the top level of our module and could not use the await keyword. Now await can be used at the top level of a module, and can be super handy when initializing imports and creating fallbacks.

Here's an example:

// Before the top-level await, JavaScript would have given you a SyntaxError with this line of code, but that is no more
await Promise.resolve(console.log("🎉"))

So until the awaited promise is resolved, the execution of the current module and the parent module that imports the current child module are deferred, but the sibling modules can be executed in the same order. Check this article out to see more examples.

#javascript #es2022 

Introduction With Basic JavaScript

The world’s most misunderstood programming language is JavaScript but JavaScript is now used by an incredible number of high-profile applications. So, it’s an important skill for any web or mobile developer to enrich the deeper knowledge in it.

Unlike most programming languages, the JavaScript language has no concept of input or output. It is designed to run as a scripting language in a host environment, and it is up to the host environment to provide mechanisms for communicating with the outside world.

Its syntax is based on the Java and C languages — many structures from those languages apply to JavaScript as well. JavaScript supports object-oriented programming with object prototypes, instead of classes. JavaScript also supports functional programming — because they are objects, functions may be stored in variables and passed around like any other object.

Let’s start off by looking at the building blocks of any language: the types. JavaScript programs manipulate values, and those values all belong to a type. JavaScript’s types are:

· Number

· String

· Boolean

· Function

· Object

· Symbol

and undefined and null, which are … slightly odd. And Array, which is a special kind of object. Date and RegExp, which are objects that you get for free. And to be technically accurate, functions are just a special type of object. So the type of diagram looks like this:

#beginner-javascript #javascript #javascript-introduction #javascript-fundamental #basic-javascritp

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What is JavaScript - Stackfindover - Blog

Who invented JavaScript, how it works, as we have given information about Programming language in our previous article ( What is PHP ), but today we will talk about what is JavaScript, why JavaScript is used The Answers to all such questions and much other information about JavaScript, you are going to get here today. Hope this information will work for you.

Who invented JavaScript?

JavaScript language was invented by Brendan Eich in 1995. JavaScript is inspired by Java Programming Language. The first name of JavaScript was Mocha which was named by Marc Andreessen, Marc Andreessen is the founder of Netscape and in the same year Mocha was renamed LiveScript, and later in December 1995, it was renamed JavaScript which is still in trend.

What is JavaScript?

JavaScript is a client-side scripting language used with HTML (Hypertext Markup Language). JavaScript is an Interpreted / Oriented language called JS in programming language JavaScript code can be run on any normal web browser. To run the code of JavaScript, we have to enable JavaScript of Web Browser. But some web browsers already have JavaScript enabled.

Today almost all websites are using it as web technology, mind is that there is maximum scope in JavaScript in the coming time, so if you want to become a programmer, then you can be very beneficial to learn JavaScript.

JavaScript Hello World Program

In JavaScript, ‘document.write‘ is used to represent a string on a browser.

<script type="text/javascript">
	document.write("Hello World!");
</script>

How to comment JavaScript code?

  • For single line comment in JavaScript we have to use // (double slashes)
  • For multiple line comments we have to use / * – – * /
<script type="text/javascript">

//single line comment

/* document.write("Hello"); */

</script>

Advantages and Disadvantages of JavaScript

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Hire Dedicated JavaScript Developers -Hire JavaScript Developers

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Does your business need an interactive website or app?

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