How to build your first ever chrome extension

How to build your first ever chrome extension

In today's blog, I will be showing you guys how to build your first-ever Chrome extension which you can use in your daily life activities. Here we will be building a simple Chrome extension which helps you to download whatsapp status from WhatsApp web in just one click.

First lets learn the basics

To build something you should have a pre-defined folder structure which manages your code and it should be readable so others can also contribute to it. In my case, I kept it as simple as possible.

Here you can see I have a manifest.json file which is the main entry point for the Chrome extension. All the details regarding your extension like version, name, permissions, and action files everything is defined here.

then we have background.js file which runs in the background in a Chrome extension. It can be used to perform tasks that need to be done continuously or at regular intervals. In manifest.json file, you declare this file as this

"background": {
    "service_worker": "background.js"

Then we have popup.html file which is the normal HTML file that is shown when you click the extension button. You can use CSS to make it looks good and add a helper javascript file for more functionalities.

Build a whatsapp status downloader extension

Now I hope you have a basic understanding of how to build a basic extension. So let's make our hands dirty with some real-life applications. We will be building a Chrome extension which downloads status from WhatsApp web.

For it let's first define the basic configuration in manifest.json file.

  "manifest_version": 3,
  "name": "whatsapp web status saver",
  "version": "1.01",
  "permissions": [
  "background": {
    "service_worker": "background.js"
  "action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icons/icon@16.png",
      "48": "icons/icon@48.png",
      "128": "icons/icon@128.png"

Here I mentioned what will be my extension name, the version of the extension, the permission required to run it, background.js file path and the icons path which will be used to display it.

Now let's define the popup.html file which will contain the HTML code for the popup which appears when you click the extension button.

<!DOCTYPE html>
    <title>WhatsApp Status Downloader</title>
    <script src="popup.js"></script>
    wait for status to load then click on download button!!
    <button id="download-btn">Download Status</button>

Next, let's define the popup.js file. There we will add a listener to our download button. Whenever that button is clicked it will send a message to Chrome runtime with the download_status message for the current tab id.

document.addEventListener("DOMContentLoaded", function() {
    const downloadBtn = document.getElementById("download-btn");
    downloadBtn.addEventListener("click", function() {
      chrome.tabs.query({ active: true, currentWindow: true }, function(tabs) {
        chrome.runtime.sendMessage({ message: "download_status", tabId: tabs[0].id });

Now let's add a listener for this download_status event. We will execute a script whenever we receive this message.

chrome.runtime.onMessage.addListener(function(request, sender, sendResponse) {
  if (request.message === "download_status") {
      target: { tabId: request.tabId },
      func: downloadStatus

As you can see I have added a listener and whenever it captures a request, it checks if request.message is the same as "download_status" or not. If yes, it invokes downloadStatus function. So let's define the function also.

function downloadStatus() {
const mediaList = document.querySelectorAll("img[src^='blob:'], video[src^='blob:']");
// Check if any media was found
if (mediaList.length === 0) {
  alert("No status media found or please wait until the status is loaded!!");
for (let i = 0; i < mediaList.length; i++) {
  const mediaUrl = mediaList[i].src;
    .then(response => response.blob())
    .then(blob => {
      const url = URL.createObjectURL(blob);
      const link = document.createElement("a");
      link.href = url; = `status_${i}.${blob.type.split("/")[1]}`;
    .catch(error => console.error(error));

It simply first select all the video and image element present in the current tab. Then first convert it to blob and make it downloadable. If no media file found, it shows an alert. That's it.

Now to test this all you have to do is go to chrome://extensions/ and enable developer mode. Then upload this folder by clicking the load unpacked button.

Now you should be able to use it. Just open WhatsApp on the web, then go to someone's status and click the extension. You can easily download their status and it will save those files in your local.

If you like to contribute in the code you can do it here on GitHub. Also if you want to directly try my extension, you can do that also by visiting here.


I hope you have now a pretty much good idea about how to build your own Chrome extension and distribute it to millions of people. I will try to come up with new ideas in the next blog also. If you enjoyed this article you can support me by buying me a coffee and following me on twitter.

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