Creating and Building Browser Extensions


Required software

Additional requirements

For building a Safari extension you have to register as a Safari Developer on Apple website and get Safari developer certificate.

Creating new project

  1. Create a directory for the project (TestExtension for example)

  2. Run with create command:

    python kango_dir/ create "path/to/TestExtension"

After running thus commands you will get extension project you can start to edit.

Adding content script

Kango allows you to run Content Scripts on any web page opened by user. Content scripts are running for each webpage shown according to @include / @exclude rules from user js metadata block as follow:

// ==UserScript==
// @name Test
// @include http://*
// ==/UserScript==

All the content scripts should be enumerated in content_scripts section of extension_info.json file.

Lets take a look on content script in work. Create content.js file inside you project common src directory (e.g. TestExtension/src/common) and place follow code in it:

// ==UserScript==
// @name Test
// @include http://*
// ==/UserScript==

var colorNumber = 0;
var colors = ['red', 'green', 'blue'];

window.setInterval(function() { = colors[colorNumber++];
    if(colorNumber > colors.length) {
        colorNumber = 0;
}, 1000);

Also add this file in content scripts array in extension_info.json in the same common directory. It should look like:

    "content_scripts": [

After building and installing the extension you will see background color blinking on every http webpage you open in your browser.

Adding background script

Background Scripts are running as long as extension is enabled in browser and executed once on each browser start.

Background scripts allows you to use all the Kango APIs in synchronous mode.

Background scripts should be enumerated in background_scripts array of extension_info.json file.

To test it on your own you can create a file named background.js in your common src directory with follow content:

var details = {
method: 'GET',
url: '',
async: true,
contentType: 'text'

kango.xhr.send(details, function(data) {
    if(data.status == 200 && data.response != null) {
    var text = data.response;
    else { // something went wrong
        kango.console.log('something went wrong');

Also add it to extension_info.json like that:

    "background_scripts": [

This will download page and output the content into console.

Adding a button into browser

To add a button to user browser you have to add browser_button section to extension_info.json file like follow:

    "browser_button": {
        "caption": "Kango",
        "tooltipText": "Kango",
        "icon": "icons/button.png"

To handle clicks on this button you have to add follow code in one of your background scripts:

kango.ui.browserButton.addEventListener(kango.ui.browserButton.event.COMMAND, function() {
    kango.console.log('Button clicked!');

Adding pop-up

You can add a pop-up window to your extension to show on button click. You can open an HTML file in pop-up and access Kango API from it.

To test how popup works create popup.html with follow content:


and add the following line to your background script:

kango.ui.browserButton.setPopup({url:'popup.html', width: 710, height:510});

Building extension

Preparing build for your extensions require you to run with build command as follow:

python kango_dir/ build "path/to/TestExtension"

After running this command you will get output directory filled with extensions builds.