JavaScript Tutorial

JS Overview

A quick overview of what JavaScript can do, how it works, and where it is used. This lesson introduces the key capabilities of JavaScript in simple, beginner-friendly language.

What Can JavaScript Do?

JavaScript makes websites interactive. It can update content, change styles, respond to user actions, validate input, and much more.

JavaScript can:

Change HTML content
Modify CSS styles
Show or hide elements
Respond to events (click, input, scroll, etc.)
Validate form input
Store data in the browser
Communicate with servers (AJAX / Fetch API)
Build full web apps using frameworks

JavaScript Works With HTML & CSS

JavaScript is one of the core technologies of the web:

HTML – Structure
CSS – Design
JavaScript – Behavior

JavaScript Engines

JavaScript runs using engines built into browsers.

Examples:

Google Chrome → V8
Firefox → SpiderMonkey
Safari → JavaScriptCore

These engines convert JS code into machine code quickly, making it fast and efficient.

JavaScript is Everywhere

Today, JavaScript is not limited to web pages.
It is used in:

Websites
Servers
Mobile apps
Desktop apps
IoT devices
Cloud functions

This makes JavaScript one of the most versatile languages in the world.

This course will teach you the basic and advanced concepts of JavaScript.

JavaScript Prerequisites

What do you need before learning JavaScript?

In order to learn JavaScript, you need to have:

Computer literacy.
Basic understanding of HTML.
Basic understanding of CSS

Note: JavaScript is single-threaded but asynchronous operations are possible.

It uses the DOM (Document Object Model) to interact with HTML elements.

Modern JavaScript uses ES6+ features like let, const, arrow functions, modules, classes, etc.

Supported by all major browsers.
Tip! JavaScript is easy to learn! Although you may struggle at first, you can reread lessons and retry coding the given examples.

   <script>
      function changeColor(element) {
         var currentColor = element.style.backgroundColor;
         if(currentColor == "red") {
            element.style.backgroundColor = "green";
         } else {
            element.style.backgroundColor = "red"; 
         }
      }
   </script>

This course contains hundreds of examples, each with the "Try It Yourself" function, making learning easier, faster and much more enjoyable. Here is just one example out of many interesting things JavaScript can do: This example shows an element that when clicked, its style (in this case, the background-color) changes.

Easier with example

EXAMPLE play_arrow Run Code

<!DOCTYPE html>
<html>
<head>
   <title> Try It Yourself </title>
   <style type="text/css">
      div {
         height: 200px;
         line-height: 200px;
         color: white;
         text-align: center;
         padding-left: 20px;
         padding-right: 20px;
      }
   </style>
</head>
<body>
   <div onclick="changeColor(this)" style="background-color: red;">
      Tap me to change my color!
   </div>

   <script>
      function changeColor(element) {
         var currentColor = element.style.backgroundColor;
         if(currentColor == "red") {
            element.style.backgroundColor = "green";
         } else {
            element.style.backgroundColor = "red"; 
         }
      }
   </script>
</body>
</html>

Output: Tap me to change my color!

Explanation

The example shows how JavaScript reacts when the user clicks the button.

The showTime() function gets the current time.

document.getElementById("demo").innerHTML updates the page content.
This demonstrates the fundament of JS: real-time interaction with the webpage without reloading.

JS Introduction chevron_right