Build Your Own Extension In Javascript

2 min readMar 1, 2023

Creating a simple browser extension in JavaScript can be a great way to get started with extension development. Here’s a step-by-step guide to creating your own browser extension in JavaScript:

Choose Your Browser: Decide which browser you want to create an extension for. Popular choices include Google Chrome, Mozilla Firefox, and Microsoft Edge.
Set Up Your Development Environment: To create a browser extension in JavaScript, you will need a text editor or an integrated development environment (IDE) such as Visual Studio Code or Sublime Text. Install the necessary tools for your chosen browser. For Chrome, you will need to download and install the Chrome Developer Tools.
Create a Manifest File: The manifest file is a JSON file that provides the browser with information about your extension, including its name, version number, and permissions. Create a new file called manifest.json and add the following code:

{
  "name": "My Extension",
  "version": "1.0",
  "manifest_version": 2,
  "description": "A simple browser extension",
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_title": "My Extension",
    "default_popup": "popup.html"
  }
}

In this code, “name” refers to the name of your extension, “version” refers to the version number, “description” is a brief description of your extension, and “permissions” lists the permissions your extension requires. The “browser_action” section defines the default behavior of your extension when clicked, and points to a popup.html file.

4. Create a Popup HTML File: The popup.html file defines the content that appears in the pop-up window when the user clicks on your extension’s icon. Create a new file called popup.html and add the following code:

<!DOCTYPE html>
<html>
  <head>
    <title>My Extension</title>
  </head>
  <body>
    <h1>Hello, world!</h1>
  </body>
</html>

This code creates a simple HTML document with a heading that reads “Hello, world!”

5. Create a JavaScript File: Create a new JavaScript file called popup.js and add the following code:

document.addEventListener("DOMContentLoaded", function() {
  var header = document.querySelector("h1");
  header.style.color = "red";
});

This code selects the h1 element in popup.html and changes its color to red when the document is loaded.

6. Load the Extension: Load your extension into your browser by navigating to chrome://extensions/ (for Chrome) or about:addons (for Firefox) and selecting “Load unpacked extension”. Navigate to the directory where your extension files are saved and select it.

7. Test Your Extension: Click on the icon for your extension in the browser toolbar to test it. You should see a pop-up window with the “Hello, world!” message in red.

Congratulations❤️! You have just created a simple browser extension in JavaScript. Now, you can go ahead and add some more functionality to it and add it to your resume.

Thank you

Build Your Own Extension In Javascript

Written by Khilesh