Hugo JS

Hugo JS

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Top 30 JavaScript Concepts You Need to Master to Become an Expert

You’ll hear many people complaining that JavaScript is weird and sometimes worthless. People complain like this because they don’t understand how things work under the hood. Although I do agree that some scenarios in JavaScript are handled differently, that does not make it weird but rather beautiful in its own way.

To start loving a programming language, you should start by looking deep within and mastering its concepts one by one.

Here is a list of 36 JavaScript concepts that you need to master to become an all-round JavaScript expert.

Although this piece is one of my longest, I assure you that it is worthy of your time. Kudos to Stephen and Leonardo for the resources.

The resources section contains a link to the GitHub repo by Leonardo which contains learning material for all these concepts explained below. Please take your time in understanding each of the below-mentioned concepts.

1. Call stack

A call stack is a mechanism for an interpreter (like the JavaScript interpreter in a web browser) to keep track of its place in a script that calls multiple functions — what function is currently being run and what functions are called from within that function, etc.

  • When a script calls a function, the interpreter adds it to the call stack and then starts carrying out the function.
  • Any functions that are called by that function are added to the call stack further up, and run where their calls are reached.
  • When the current function is finished, the interpreter takes it off the stack and resumes execution where it left off in the last code listing.
  • If the stack takes up more space than it had assigned to it, it results in a "stack overflow" error.

Example

function greeting() {
   // [1] Some code here
   sayHi();
   // [2] Some code here
}
function sayHi() {
   return "Hi!";
}

// Invoke the `greeting` function
greeting();

// [3] Some code here

2. Primitive Data Types

const foo = "bar";
foo.length; // 3
foo === "bar"; // true

When you assign the value bar to the constant foo, it is of the primitive type string. That’s acceptable for everyone. But how can you access the property length of a primitive string?

Weird? Nah.

This feature is called autoboxing. In the above example, JavaScript wraps the constant in a temporary wrapper object and then accesses the length property of that object. Once this step is complete, the object is safely discarded.

By having a deep knowledge of the primitive data types, you will know how they are stored in memory up until the point of their binary representation. You will also know how these “weird” situations occur and the logical reason behind them.

3. Value Types and Reference Types

I recently had some confusion over how the concept “pass by reference” works in JavaScript. Although I was aware of the concepts “pass by reference” and “pass by value” in languages such as C and Java, I was not sure how it worked in JavaScript.

Did you know that variables assigned to non-primitive values in JavaScript are given a reference to that value? The reference points to the memory location where the value is stored.

var arr1 = [1,2,3];

var arr2 = arr1;
arr2.push(10);
console.log(arr2);
//[1, 2, 3, 10]
console.log(arr1);
//[1, 2, 3, 10]

As you can see from the above example, any modifications done to arr2 will be reflected on arr1 as well. This is because they only hold the reference to the value, not the actual value itself.

By understanding this concept of value types and reference types, you will have a better understanding of how variables are assigned with values and memory references.

4. Forced type conversion

This concept mainly explains the difference between implicit and explicit coercion. This is one of the few areas where you can go wrong when using JavaScript. This is especially true for the concept of implicit type conversion, because it behaves differently for different data types.

This is one of the most frequently interviewed content in JavaScript interviews.

Number('789')//Explicit conversion
+'789'//implicit conversion
789 != '456'//implicit conversion
9> '5'//implicit conversion
10/null//implicit conversion
true | 0//implicit conversion

By clearly understanding type conversion, then you have learned one of JavaScript's most difficult concepts.

5. Equality comparison and the'typeof' operator

This concept basically explains the use of double and triple equal signs, and when and why they are used. Although on the surface they are the same and will give the same results most of the time, if you use them without your knowledge, they may bring you unexpected errors.

You should also be able to use the typeof operator and know the possibility of output. But when there are objects, it can be confusing.

typeof 3//"number"
typeof "abc"//"string"
typeof {}//"object"
typeof true//"boolean"
typeof undefined//"undefined"
typeof function(){}//"function"
typeof []//"object"
typeof null//"object"

6, JavaScript scope

Scope is a concept, and I believe that you should understand it at the beginning of your JS journey. According to Wissam, the simple definition of scope is that when the compiler needs a variable and function, it is the place to look for that variable and function.

Understanding scope will allow you to use JavaScript more effectively. You should understand global scope, block and function scope, also known as lexical scope.

JS scope can be confusing at first, but once you understand how it works, using it can be very exciting.

7. Statements and expressions

These are the two main grammatical categories in JavaScript. You should know the difference between the two and how the statement is calculated. This will allow you to fully understand how the code is structured into expressions and statements.

You will notice that most of your code is expressions, and relatively speaking, you use fewer statements. You can also avoid errors caused by incorrect use of these two methods.

8. Immediately call function expressions and modules

A function expression called immediately is a function that runs immediately after it is defined. They are mainly used to avoid polluting the global scope.

Later, the ES6 module was introduced, providing a standard way to avoid global scope pollution, although some people think it is not a direct replacement for IIFEs.

By understanding IIFEs and modules, you can encounter fewer errors due to improper handling of the global scope when developing applications. However, with modules, you can do many things.

9. Message queue and event loop

As the MDN documentation says, JavaScript has a concurrency model based on the event loop, which is responsible for executing code, collecting and processing events, and executing queued subtasks. This model is very different from the models in other languages ​​(such as C and Java).

In the above concurrency model, the message queue is used to process messages starting from the oldest message. As long as the event occurs and there is an event listener listening to it, the message will be added to the queue.

By understanding these concepts, you can better understand how JS works under the hood and how to interpret your code.

10. Time interval

To dispatch a call or function in JavaScript, two methods can be used.

  • setTimeout allows us to run the function once after a specific time interval.
  • setInterval allows us to run a function repeatedly, start running after a specific time interval, and then continue to run repeatedly within that time interval.

These are somewhat related to the previous concepts of message queues and event handlers. Therefore, by understanding time interval methods, we can understand how they work and use them effectively in our use cases.

11. JavaScript engine

We are now delving into JavaScript. The JavaScript engine is a computer program or interpreter that executes JavaScript code. The JavaScript engine can be written in multiple languages.

For example, the V8 engine that drives the Chrome browser is written in C, and the SpiderMonkey engine that drives the Firefox browser is written in C and C.

It is very important for you to understand which JavaScript engine you are using to write efficient code. Mobile developers using webview should pay special attention to this.

12. Bit operation

These operations treat values ​​as bits (0 and 1), rather than decimal, hexadecimal, or octal numbers. Bit operators perform operations on this binary representation, but they return standard JavaScript values.

Normally, you don't use these operations in your code, but they do have some use cases. You can use them to find even and odd values, color conversion, color extraction, and configuration flags.

By thoroughly understanding these bit operations, you can make good use of technologies such as WebGL, because it contains many pixel operations.

13. DOM and layout tree

Most people have heard of the Document Object Model (DOM), but only a few people know it deeply. Did you know that what you see in the browser is not the DOM? It is the render tree, which is actually a combination of DOM and CSSOM.

By understanding the working principle and structure of the DOM, and how the page is presented, we can dynamically manipulate web pages with the help of JavaScript. This is especially necessary to ensure that our applications have high standards of performance.

14. Classes and factories

JavaScript is not an object-oriented language. However, in order to simulate OOP properties, a constructor is used. According to Tania, "Classes in JavaScript don't actually provide additional functionality, and are often described as providing syntactic sugar on top of prototypes and inheritance because they provide cleaner and more elegant syntax.

Other programming languages ​​use classes, so the class syntax in JavaScript makes it easier for developers to switch between different languages. "

A factory function is a function that is not a class or constructor but returns an object. JS master Eric Elliot said: "In JavaScript, any function can return a new object. When it is not a constructor or a class, it is called a factory function."

You should have a good understanding of these two concepts, especially when you start developing larger applications.

15. "this" keyword and, "apply", "call" and "bind" methods

I personally think that it is vital for a JS developer to understand this keyword. If you cannot understand it correctly, your application will encounter various problems later.

If you thishave a good understanding of keywords, then you can pay attention to apply, calland bindmethods.

These methods are necessary to call functions with appropriate context. You will especially need bindmethods when passing callbacks that access this . I learned this while helping a friend debug his code!

16. Constructor and'instanceOf' operator

The constructor is just like a regular function. But they have many differences. By convention, function names start with an uppercase letter and can only be executed with the new operator.

Programmers with an OOP background should be familiar with this new keyword.

To correctly identify the type of object, we use the instanceOf operator. Simply put, it checks whether an object is an instance of another object.

This will help you understand how objects inherit from each other. Inheritance is achieved through prototypes.

17. Prototype

This is one of the most confusing concepts in JavaScript, even for people with ten years of experience.

Prototypes in JavaScript are mechanisms for sharing common functions between objects. Almost all objects in JavaScript are instances of Object. A typical object inherits Object.prototypeall the properties and methods in.

Simply put, a prototype is an object from which a JavaScript object inherits methods and properties.

By better understanding the prototype, you can build efficient and fast applications.

18. Create objects with'new','Object.create', and'Object.assign'

There are many ways to create objects in JavaScript. But some people choose Object.createnot to use newkeywords for a reason.

When Object.createcreating, you can use an existing object as the prototype of the newly created object. This will allow the reuse of existing object properties and functions, a bit like the concept of inheritance in OOP.

When you use Object.assignmethods, you can copy enumerable own properties from one or more source objects to the target object. In this case, the prototype of the target object does not contain the properties of the source object.

This is the main difference between these two methods.

By understanding these three methods of creating objects, you can appropriately use them in your application according to the use case to create memory-efficient programs.

19.'map','filter', and'reduce' methods

These three methods are very useful when it comes to array operations. They can be found in the prototype of the array.

If you have an array and you want to do something with each element, then you can use mapmethods.

If you have an array and want to run a condition on each element and get the value passing the condition, you can use the filtermethod.

reduceThe method performs a reducer function on all elements of the array, and finally returns a value. A perfect example is to get the sum of all elements in an array.

let numbers = [1,2,3,4,5,6] const reduced = numbers.reduce((accumulator, currentValue) => accumulator + currentValue) console.log(reduced) //21

Note that the above three methods will not change the value of the original array.

20, pure functions, side effects and state changes

These three concepts are very important to JavaScript developers. State changes are especially important for developers who use React.

A pure function always returns a value consistent with the input provided, without accessing or changing any variables outside of its scope. This type of function is easier to read, debug, and test.

A side effect is a piece of code where a variable is created and available in the entire scope when it is not needed. If your function accesses variables outside the scope, there will be a side effect.

State change refers to changing the value of a variable. If you change a variable, it may affect other functions based on its previous value. In a react environment, it is recommended that you do not change your state. Here is a good article on immutability.

21, closure

Closures are difficult to understand. But once you understand it, you will begin to see the beauty of JavaScript. There are abundant resources online. Just make sure you take the time to learn closures.

Closures allow you to access the scope of external functions in the internal scope. Every time a function is created, a JavaScript closure is created.

Understand why you should use closures in order to understand them more deeply.

22, higher-order functions

Higher-order functions are functions that take other functions as parameters or return functions. Higher-order functions allow synthesis to release maximum energy. You can create smaller functions that only handle one task, and then construct complex functions with the help of these smaller functions. This will also increase the reusability of the code.

This also reduces errors and makes our code easier to read and understand.

23, recursion

Recursion is a common concept in all programming languages. Simply put, recursion is the concept of breaking down big problems into small ones.

In practice, this usually means writing a function that calls itself. Although recursion may be a confusing concept that gives you a headache, with a lot of practice and starting with some small problems, you can understand it better.

But be aware that if you accidentally use recursion, you may encounter stack overflow errors. As an exercise, do some research on this error. You need to modify the knowledge about the first topic, the call stack, to fully understand the context of this error.

24. Collection and generator functions

Collection and generator functions are newly introduced in ES6. The new collection is introduced Map, Set, WeakSetand WeakMap. These collections provide you with some very good use cases. You must understand their usage, especially when using modern JavaScript.

On the other hand, generator functions are sometimes a bit tricky to understand, especially for beginners.

Generators allow you to write code functions, enabling you to pause and restart functions without blocking the execution of other code, which is very rare in JavaScript.

25, Promises

Jacqueline explained Promises: "Imagine you are a child. Your mother promises you that she will buy you a new phone next week."

You won’t know if you can get that phone until next week. Either your mother actually bought you a brand new phone, or she didn't buy it because she was unhappy.

This is one Promise. PromiseThere are three states. They are:

  • Pending: You don't know if you will get that call.
  • Fulfilled: Mom is very happy, she bought you a brand new mobile phone.
  • Rejected: Mom is not happy, she won't buy you a mobile phone.

So far, this is Promisethe simplest and clearest explanation I have given. Honestly, I learned this while doing a demo projectPromise the concepts .

This makes it difficult for me to understand what happened because I don't know Promisewhat it is. Fast forward to now. Thanks to the abundant resources on the Internet, I have Promisea better understanding. Combined with my working knowledge of the project, I can have a clear understanding.

26, asynchronous programming

To understand what asynchronous programming is, we should first refresh the knowledge of synchronous programming. Synchronous programming is thread-blocking. Since JavaScript is single-threaded, the code will be executed line by line.

But with asynchronous code, you can execute long-term network requests without blocking the main thread. This is especially useful when you have to perform multiple tasks that take a long time to complete.

But in some cases, you may need to block the thread, even for a very long task. The async/awaitconcepts you will use at this time .

Learning these concepts well will allow you to write programs that execute efficiently, even if there are many tasks running.

27, ES6 arrow function

Arrow function is an additional feature of ES6, which replaces regular functions in syntax. The difference is that the arrow is not bound to the function this, arguments, superor new.targetkeyword.

This makes the arrow a good choice in some situations, but a terrible choice in others.

Therefore, never get into the habit of using arrow functions. Implement them according to your use case.

28, data structure

No matter which programming language is used, data structure is one of the basic knowledge that developers should have.

"Bad programmers worry about code. Good programmers worry about data structures and their relationships." Linus Torvalds, creator of Linux and Git

By in-depth understanding of different data structures, you can build efficient programs that run well in different environments. You should understand linked lists, queues, stacks, trees, graphs, and hash tables.

29, time complexity

Time complexity analysis is another basic principle of computer programming, which has nothing to do with programming languages. To build better applications, you should write better solutions. In order to do this, you should understand the concept of time complexity. It is sometimes called the Big O.

The big O symbol describes the execution time or space used by the algorithm. The big O symbol specifically describes the worst-case scenario.

This will allow you to choose and implement the best performing algorithm, even in the worst case.

30. Algorithm

This is one of the first things you will learn in a computer science course. In short, an algorithm is a process of gradually achieving a goal. The programmer should be able to look at any problem from the point of view of the algorithm.

They should be able to build problems and solutions step by step. This algorithm is the program you will write later.

Although there are thousands of use cases for the algorithm, two of the use cases are quite common:

  • search for
  • Sort

These two use cases are very common to programmers, and you should at least fully understand the known algorithms available to them. There is no fixed rule that you should use one of these algorithms, but these algorithms are well known in terms of performance and well documented.

You can even create your own algorithm and introduce it to the world. If it is better than the currently known algorithm, you may become the next programming star!

#angular #javascript #react #programming #nodejs

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Top 30 JavaScript Concepts You Need to Master to Become an Expert

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Hugo JS

Hugo JS

1595376540

Top 30 JavaScript Concepts You Need to Master to Become an Expert

You’ll hear many people complaining that JavaScript is weird and sometimes worthless. People complain like this because they don’t understand how things work under the hood. Although I do agree that some scenarios in JavaScript are handled differently, that does not make it weird but rather beautiful in its own way.

To start loving a programming language, you should start by looking deep within and mastering its concepts one by one.

Here is a list of 36 JavaScript concepts that you need to master to become an all-round JavaScript expert.

Although this piece is one of my longest, I assure you that it is worthy of your time. Kudos to Stephen and Leonardo for the resources.

The resources section contains a link to the GitHub repo by Leonardo which contains learning material for all these concepts explained below. Please take your time in understanding each of the below-mentioned concepts.

1. Call stack

A call stack is a mechanism for an interpreter (like the JavaScript interpreter in a web browser) to keep track of its place in a script that calls multiple functions — what function is currently being run and what functions are called from within that function, etc.

  • When a script calls a function, the interpreter adds it to the call stack and then starts carrying out the function.
  • Any functions that are called by that function are added to the call stack further up, and run where their calls are reached.
  • When the current function is finished, the interpreter takes it off the stack and resumes execution where it left off in the last code listing.
  • If the stack takes up more space than it had assigned to it, it results in a "stack overflow" error.

Example

function greeting() {
   // [1] Some code here
   sayHi();
   // [2] Some code here
}
function sayHi() {
   return "Hi!";
}

// Invoke the `greeting` function
greeting();

// [3] Some code here

2. Primitive Data Types

const foo = "bar";
foo.length; // 3
foo === "bar"; // true

When you assign the value bar to the constant foo, it is of the primitive type string. That’s acceptable for everyone. But how can you access the property length of a primitive string?

Weird? Nah.

This feature is called autoboxing. In the above example, JavaScript wraps the constant in a temporary wrapper object and then accesses the length property of that object. Once this step is complete, the object is safely discarded.

By having a deep knowledge of the primitive data types, you will know how they are stored in memory up until the point of their binary representation. You will also know how these “weird” situations occur and the logical reason behind them.

3. Value Types and Reference Types

I recently had some confusion over how the concept “pass by reference” works in JavaScript. Although I was aware of the concepts “pass by reference” and “pass by value” in languages such as C and Java, I was not sure how it worked in JavaScript.

Did you know that variables assigned to non-primitive values in JavaScript are given a reference to that value? The reference points to the memory location where the value is stored.

var arr1 = [1,2,3];

var arr2 = arr1;
arr2.push(10);
console.log(arr2);
//[1, 2, 3, 10]
console.log(arr1);
//[1, 2, 3, 10]

As you can see from the above example, any modifications done to arr2 will be reflected on arr1 as well. This is because they only hold the reference to the value, not the actual value itself.

By understanding this concept of value types and reference types, you will have a better understanding of how variables are assigned with values and memory references.

4. Forced type conversion

This concept mainly explains the difference between implicit and explicit coercion. This is one of the few areas where you can go wrong when using JavaScript. This is especially true for the concept of implicit type conversion, because it behaves differently for different data types.

This is one of the most frequently interviewed content in JavaScript interviews.

Number('789')//Explicit conversion
+'789'//implicit conversion
789 != '456'//implicit conversion
9> '5'//implicit conversion
10/null//implicit conversion
true | 0//implicit conversion

By clearly understanding type conversion, then you have learned one of JavaScript's most difficult concepts.

5. Equality comparison and the'typeof' operator

This concept basically explains the use of double and triple equal signs, and when and why they are used. Although on the surface they are the same and will give the same results most of the time, if you use them without your knowledge, they may bring you unexpected errors.

You should also be able to use the typeof operator and know the possibility of output. But when there are objects, it can be confusing.

typeof 3//"number"
typeof "abc"//"string"
typeof {}//"object"
typeof true//"boolean"
typeof undefined//"undefined"
typeof function(){}//"function"
typeof []//"object"
typeof null//"object"

6, JavaScript scope

Scope is a concept, and I believe that you should understand it at the beginning of your JS journey. According to Wissam, the simple definition of scope is that when the compiler needs a variable and function, it is the place to look for that variable and function.

Understanding scope will allow you to use JavaScript more effectively. You should understand global scope, block and function scope, also known as lexical scope.

JS scope can be confusing at first, but once you understand how it works, using it can be very exciting.

7. Statements and expressions

These are the two main grammatical categories in JavaScript. You should know the difference between the two and how the statement is calculated. This will allow you to fully understand how the code is structured into expressions and statements.

You will notice that most of your code is expressions, and relatively speaking, you use fewer statements. You can also avoid errors caused by incorrect use of these two methods.

8. Immediately call function expressions and modules

A function expression called immediately is a function that runs immediately after it is defined. They are mainly used to avoid polluting the global scope.

Later, the ES6 module was introduced, providing a standard way to avoid global scope pollution, although some people think it is not a direct replacement for IIFEs.

By understanding IIFEs and modules, you can encounter fewer errors due to improper handling of the global scope when developing applications. However, with modules, you can do many things.

9. Message queue and event loop

As the MDN documentation says, JavaScript has a concurrency model based on the event loop, which is responsible for executing code, collecting and processing events, and executing queued subtasks. This model is very different from the models in other languages ​​(such as C and Java).

In the above concurrency model, the message queue is used to process messages starting from the oldest message. As long as the event occurs and there is an event listener listening to it, the message will be added to the queue.

By understanding these concepts, you can better understand how JS works under the hood and how to interpret your code.

10. Time interval

To dispatch a call or function in JavaScript, two methods can be used.

  • setTimeout allows us to run the function once after a specific time interval.
  • setInterval allows us to run a function repeatedly, start running after a specific time interval, and then continue to run repeatedly within that time interval.

These are somewhat related to the previous concepts of message queues and event handlers. Therefore, by understanding time interval methods, we can understand how they work and use them effectively in our use cases.

11. JavaScript engine

We are now delving into JavaScript. The JavaScript engine is a computer program or interpreter that executes JavaScript code. The JavaScript engine can be written in multiple languages.

For example, the V8 engine that drives the Chrome browser is written in C, and the SpiderMonkey engine that drives the Firefox browser is written in C and C.

It is very important for you to understand which JavaScript engine you are using to write efficient code. Mobile developers using webview should pay special attention to this.

12. Bit operation

These operations treat values ​​as bits (0 and 1), rather than decimal, hexadecimal, or octal numbers. Bit operators perform operations on this binary representation, but they return standard JavaScript values.

Normally, you don't use these operations in your code, but they do have some use cases. You can use them to find even and odd values, color conversion, color extraction, and configuration flags.

By thoroughly understanding these bit operations, you can make good use of technologies such as WebGL, because it contains many pixel operations.

13. DOM and layout tree

Most people have heard of the Document Object Model (DOM), but only a few people know it deeply. Did you know that what you see in the browser is not the DOM? It is the render tree, which is actually a combination of DOM and CSSOM.

By understanding the working principle and structure of the DOM, and how the page is presented, we can dynamically manipulate web pages with the help of JavaScript. This is especially necessary to ensure that our applications have high standards of performance.

14. Classes and factories

JavaScript is not an object-oriented language. However, in order to simulate OOP properties, a constructor is used. According to Tania, "Classes in JavaScript don't actually provide additional functionality, and are often described as providing syntactic sugar on top of prototypes and inheritance because they provide cleaner and more elegant syntax.

Other programming languages ​​use classes, so the class syntax in JavaScript makes it easier for developers to switch between different languages. "

A factory function is a function that is not a class or constructor but returns an object. JS master Eric Elliot said: "In JavaScript, any function can return a new object. When it is not a constructor or a class, it is called a factory function."

You should have a good understanding of these two concepts, especially when you start developing larger applications.

15. "this" keyword and, "apply", "call" and "bind" methods

I personally think that it is vital for a JS developer to understand this keyword. If you cannot understand it correctly, your application will encounter various problems later.

If you thishave a good understanding of keywords, then you can pay attention to apply, calland bindmethods.

These methods are necessary to call functions with appropriate context. You will especially need bindmethods when passing callbacks that access this . I learned this while helping a friend debug his code!

16. Constructor and'instanceOf' operator

The constructor is just like a regular function. But they have many differences. By convention, function names start with an uppercase letter and can only be executed with the new operator.

Programmers with an OOP background should be familiar with this new keyword.

To correctly identify the type of object, we use the instanceOf operator. Simply put, it checks whether an object is an instance of another object.

This will help you understand how objects inherit from each other. Inheritance is achieved through prototypes.

17. Prototype

This is one of the most confusing concepts in JavaScript, even for people with ten years of experience.

Prototypes in JavaScript are mechanisms for sharing common functions between objects. Almost all objects in JavaScript are instances of Object. A typical object inherits Object.prototypeall the properties and methods in.

Simply put, a prototype is an object from which a JavaScript object inherits methods and properties.

By better understanding the prototype, you can build efficient and fast applications.

18. Create objects with'new','Object.create', and'Object.assign'

There are many ways to create objects in JavaScript. But some people choose Object.createnot to use newkeywords for a reason.

When Object.createcreating, you can use an existing object as the prototype of the newly created object. This will allow the reuse of existing object properties and functions, a bit like the concept of inheritance in OOP.

When you use Object.assignmethods, you can copy enumerable own properties from one or more source objects to the target object. In this case, the prototype of the target object does not contain the properties of the source object.

This is the main difference between these two methods.

By understanding these three methods of creating objects, you can appropriately use them in your application according to the use case to create memory-efficient programs.

19.'map','filter', and'reduce' methods

These three methods are very useful when it comes to array operations. They can be found in the prototype of the array.

If you have an array and you want to do something with each element, then you can use mapmethods.

If you have an array and want to run a condition on each element and get the value passing the condition, you can use the filtermethod.

reduceThe method performs a reducer function on all elements of the array, and finally returns a value. A perfect example is to get the sum of all elements in an array.

let numbers = [1,2,3,4,5,6] const reduced = numbers.reduce((accumulator, currentValue) => accumulator + currentValue) console.log(reduced) //21

Note that the above three methods will not change the value of the original array.

20, pure functions, side effects and state changes

These three concepts are very important to JavaScript developers. State changes are especially important for developers who use React.

A pure function always returns a value consistent with the input provided, without accessing or changing any variables outside of its scope. This type of function is easier to read, debug, and test.

A side effect is a piece of code where a variable is created and available in the entire scope when it is not needed. If your function accesses variables outside the scope, there will be a side effect.

State change refers to changing the value of a variable. If you change a variable, it may affect other functions based on its previous value. In a react environment, it is recommended that you do not change your state. Here is a good article on immutability.

21, closure

Closures are difficult to understand. But once you understand it, you will begin to see the beauty of JavaScript. There are abundant resources online. Just make sure you take the time to learn closures.

Closures allow you to access the scope of external functions in the internal scope. Every time a function is created, a JavaScript closure is created.

Understand why you should use closures in order to understand them more deeply.

22, higher-order functions

Higher-order functions are functions that take other functions as parameters or return functions. Higher-order functions allow synthesis to release maximum energy. You can create smaller functions that only handle one task, and then construct complex functions with the help of these smaller functions. This will also increase the reusability of the code.

This also reduces errors and makes our code easier to read and understand.

23, recursion

Recursion is a common concept in all programming languages. Simply put, recursion is the concept of breaking down big problems into small ones.

In practice, this usually means writing a function that calls itself. Although recursion may be a confusing concept that gives you a headache, with a lot of practice and starting with some small problems, you can understand it better.

But be aware that if you accidentally use recursion, you may encounter stack overflow errors. As an exercise, do some research on this error. You need to modify the knowledge about the first topic, the call stack, to fully understand the context of this error.

24. Collection and generator functions

Collection and generator functions are newly introduced in ES6. The new collection is introduced Map, Set, WeakSetand WeakMap. These collections provide you with some very good use cases. You must understand their usage, especially when using modern JavaScript.

On the other hand, generator functions are sometimes a bit tricky to understand, especially for beginners.

Generators allow you to write code functions, enabling you to pause and restart functions without blocking the execution of other code, which is very rare in JavaScript.

25, Promises

Jacqueline explained Promises: "Imagine you are a child. Your mother promises you that she will buy you a new phone next week."

You won’t know if you can get that phone until next week. Either your mother actually bought you a brand new phone, or she didn't buy it because she was unhappy.

This is one Promise. PromiseThere are three states. They are:

  • Pending: You don't know if you will get that call.
  • Fulfilled: Mom is very happy, she bought you a brand new mobile phone.
  • Rejected: Mom is not happy, she won't buy you a mobile phone.

So far, this is Promisethe simplest and clearest explanation I have given. Honestly, I learned this while doing a demo projectPromise the concepts .

This makes it difficult for me to understand what happened because I don't know Promisewhat it is. Fast forward to now. Thanks to the abundant resources on the Internet, I have Promisea better understanding. Combined with my working knowledge of the project, I can have a clear understanding.

26, asynchronous programming

To understand what asynchronous programming is, we should first refresh the knowledge of synchronous programming. Synchronous programming is thread-blocking. Since JavaScript is single-threaded, the code will be executed line by line.

But with asynchronous code, you can execute long-term network requests without blocking the main thread. This is especially useful when you have to perform multiple tasks that take a long time to complete.

But in some cases, you may need to block the thread, even for a very long task. The async/awaitconcepts you will use at this time .

Learning these concepts well will allow you to write programs that execute efficiently, even if there are many tasks running.

27, ES6 arrow function

Arrow function is an additional feature of ES6, which replaces regular functions in syntax. The difference is that the arrow is not bound to the function this, arguments, superor new.targetkeyword.

This makes the arrow a good choice in some situations, but a terrible choice in others.

Therefore, never get into the habit of using arrow functions. Implement them according to your use case.

28, data structure

No matter which programming language is used, data structure is one of the basic knowledge that developers should have.

"Bad programmers worry about code. Good programmers worry about data structures and their relationships." Linus Torvalds, creator of Linux and Git

By in-depth understanding of different data structures, you can build efficient programs that run well in different environments. You should understand linked lists, queues, stacks, trees, graphs, and hash tables.

29, time complexity

Time complexity analysis is another basic principle of computer programming, which has nothing to do with programming languages. To build better applications, you should write better solutions. In order to do this, you should understand the concept of time complexity. It is sometimes called the Big O.

The big O symbol describes the execution time or space used by the algorithm. The big O symbol specifically describes the worst-case scenario.

This will allow you to choose and implement the best performing algorithm, even in the worst case.

30. Algorithm

This is one of the first things you will learn in a computer science course. In short, an algorithm is a process of gradually achieving a goal. The programmer should be able to look at any problem from the point of view of the algorithm.

They should be able to build problems and solutions step by step. This algorithm is the program you will write later.

Although there are thousands of use cases for the algorithm, two of the use cases are quite common:

  • search for
  • Sort

These two use cases are very common to programmers, and you should at least fully understand the known algorithms available to them. There is no fixed rule that you should use one of these algorithms, but these algorithms are well known in terms of performance and well documented.

You can even create your own algorithm and introduce it to the world. If it is better than the currently known algorithm, you may become the next programming star!

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The essential JavaScript concepts that you should understand

As a JavaScript developer of any level, you need to understand its foundational concepts and some of the new ideas that help us developing code. In this article, we are going to review 16 basic concepts. So without further ado, let’s get to it.

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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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