What is JavaScript Introduction Explained

What is JavaScript?

JavaScript is a powerful and flexible programming language that runs right inside your web browser. It brings life to static HTML pages by adding interactivity and dynamic features.

Imagine a basic webpage with just text and images—JavaScript turns that into something you can interact with: buttons that respond when clicked, forms that check your input, sliders that move, animations that play, and much more.

Why is JavaScript Important?

JavaScript is one of the three core technologies of the web, alongside HTML and CSS:

  • HTML defines the content and structure.

  • CSS styles and designs the layout.

  • JavaScript makes it interactive and functional.

With JavaScript, you can:

  • Build modern web and mobile apps

  • Create animations and effects

  • Make games that run in the browser

  • Develop server-side apps using tools like Node.js

  • Handle user inputs and form validations

  • Modify HTML and CSS dynamically in response to user actions

In short: no modern website is complete without JavaScript—it's used everywhere!

JavaScript in Action – A Simple Example

Here's a basic example of how JavaScript can make a webpage interactive. The following form uses JavaScript to validate input and change the form's color when clicked.

    <!DOCTYPE html>
    <html>
    <head>
    <title>Simple Form Example</title>
    <style>
        #userForm {
        padding: 10px;
        border: 1px solid #ccc;
        }
    </style>
    </head>
    <body>

    <h2>User Information Form</h2>

    <form id="userForm">
    First Name: <input type="text" id="firstName"><br><br>
    Middle Name: <input type="text"><br><br>
    Last Name: <input type="text"><br><br>
    Date of Birth: <input type="date"><br><br>
    Address: <input type="text"><br><br>
    City: <input type="text"><br><br>
    Zip Code: <input type="text"><br><br>
    <button type="button" onclick="validateForm()">Submit</button>
    </form>

    <script>
    function validateForm() {
        let name = document.getElementById("firstName").value;
        if (name === "") {
        alert("Please enter your first name.");
        } else {
        document.getElementById("userForm").style.backgroundColor = "#e0f7fa";
        alert("Form submitted successfully!");
        }
    }
    </script>

    </body>
    </html>

What’s Happening Here?

  • If the first name field is empty, the user sees an alert.

  • If it’s filled in, the background color of the form changes, and a success message is shown.

  • This is just a small taste of what JavaScript can do!

A Brief History of JavaScript

JavaScript was created in 1995 by Brendan Eich while working at Netscape. It was originally called Mocha, then renamed to LiveScript, and finally became known as JavaScript.

Despite the name, JavaScript has nothing to do with Java—they are completely different languages. The name was mainly a marketing move during Java’s popularity boom.

Over time, JavaScript has evolved dramatically. Today, it doesn't just run in browsers—it can also run on servers, mobile devices, and even IoT hardware using environments like Node.js.

JavaScript vs ECMAScript: What’s the Difference?

While learning JavaScript, you might hear the term ECMAScript (or ES) a lot. Here's the simple explanation:

  • JavaScript is the programming language we use.

  • ECMAScript is the official standard that defines how JavaScript should work.

Think of ECMAScript as the blueprint, and JavaScript as the real-world implementation of that blueprint.

To make sure JavaScript behaves the same way in all browsers, the ECMA International organization maintains the ECMAScript specification (also known as ECMA-262).

ECMAScript Versions

Each version adds new features to the language. Here are some major versions:

  • ES5 (2009) – widely supported and still common today

  • ES6 / ES2015 – introduced modern syntax (like let, const, arrow functions, classes)

  • ES7 to ES12 (2016–2021) – added async/await, array includes, optional chaining, etc.

 JavaScript Engines: How JavaScript Runs

Every browser has its own JavaScript engine to run code. Here’s a quick overview:

BrowserJavaScript Engine
Google Chrome / Edge (Chromium)V8
Mozilla FirefoxSpiderMonkey
SafariJavaScriptCore (a.k.a. Nitro)





These engines interpret or compile JavaScript into machine code that your computer can understand—making everything work smoothly in real time.