JavaScript

JavaScript (JS) is the world’s most popular lightweight, interpreted compiled programming language. It is also known as a scripting language for web pages. It can be used for Client-side as well as Server-side developments.

JavaScript Tutorial

JavaScript can be added to your HTML file in two ways:

Internal JavaScript: We can add JS code directly to our HTML file by writing the code inside the <script> tag. The <script> tag can either be placed inside the <head> or the <body> tag according to the requirement.
External JavaScript File: We can create a file with .js extension and paste the JS code inside it. After creating the file, add this file in <script src=”file_name.js”> tag inside <head> tag of the HTML file.

Syntax: It is the basic syntax to write code.


<script>
    // JS Code
</script>

Example 1: It is the basic example to embed JS code in an HTML file.


<!DOCTYPE html>
<html lang="en">

<head>
    <title>
        Basic Example to Describe JavaScript
    </title>
</head>

<body>

    <!-- JavaScript code can be embedded inside
        head section or body section -->
    <script>
        console.log("Welcome to GeeksforGeeks");
    </script>
</body>

</html>

Output: The output will display on console.

Welcome to GeeksforGeeks

Example 2: This example describes a simple function and prints the values.


<script>
 
    // Declare a variable and initialize it
    // Global variable declaration
    var Name = "Apple";
 
    // Function definition
    function MyFunction() {
 
        // Local variable declaration
        var num = 45;
 
        // Console value of Global variable
        console.log(Name);
 
        // Console value of local variable
        console.log("\n" + num);
    }
     
    // Function call
    MyFunction();
</script>

Output: Console output

Apple
45

Why JavaScript is used?

JavaScript is the most popular programming language for both client-side and server-side to make interactive web pages. It is mainly used to develop websites and web-based applications.

Creating Interactive Websites: JavaScript is used to make the web pages dynamic and interactive. It means using JavaScript, we can change the web page content and styles dynamically.
Building Applications: JavaScript is used to make web and mobile applications. To build the web and mobile apps, we can use most popular JavaScript frameworks like – ReactJS, React Native, Node.js etc.
Web Servers: We can make robust server applications using JavaScript. To be precise we use JavaScript frameworks like Node.js and Express.js to build these servers.
Game Development: JavaSCript can be used to design Browser games. In JavaScript, lots of game engines available that provide frameworks for building games.

How JavaScript is different from HTML?

JavaScript is an advanced programming language that makes web pages more interactive and dynamic whereas HTML is a standard markup language that provides the primary structure of a website.
JavaScript simply adds dynamic content to websites to make them look good and HTML work on the look of the website without the interactive effects and all.
JavaScript manipulates the content to create dynamic web pages whereas HTML pages are static which means the content cannot be changed.
JavaScript is not cross-browser compatible whereas HTML is cross-browser compatible.
JavaScript can be embedded inside HTML but HTML can not be embedded inside JavaScript.

Why to learn JavaScript ?

JavaScript is the most popular and hence the most loved language around the globe. Apart from this, there are abundant reasons to learn it. Below are a listing of few important points:

No need of compilers: Since JavaScript is an interpreted language, therefore it does not need any compiler for compilations.
Used both Client and Server-side: Earlier JavaScript was used to build client-side applications only, but with the evolution of its frameworks namely Node.js and Express.js, it is now widely used for building server-side applications too.
Helps to build a complete solution: As we saw, JavaScript is widely used in both client and server-side applications, therefore it helps us to build an end-to-end solution to a given problem.
Used everywhere: JavaScript is so loved because it can be used anywhere. It can be used to develop websites, games or mobile apps, etc.
Huge community support: JavaScript has a huge community of users and mentors who love this language and take it’s legacy forward.

Learn more about JavaScript

JavaScript Objects Complete Reference

This section contains the list of all properties and methods of all JavaScript objects.

JavaScript Interview Questions

JavaScript Practice Quiz

JavaScript Questions

Please go through the JavaScript Examples link to see the wide collection of JavaScript programming examples. The examples are categorized based on the topics, including objects, functions, arrays, DOM, and many more.

JavaScript – GeeksforGeeks