Building a cross browser extension with JS

Karthickeyan Narasimhan

Software Developer @ Freshworks Inc.

Mozilla Tech Speaker

Mozilla Rep

Hi.

We’re Mozilla, the proudly non-profit champions of the Internet, helping to keep it healthy, open and accessible to all.

Browser Add-ons
WebExtensions
Anatomy of WebExtensions
Building your first Add-on

Agenda

Browser Add-ons extend and modify the functionality of the browser.

Browser Add-ons?

Firefox is the most customizable browser!

1 Million+ addons downloaded everyday

70+ Add-ons published everyday

250 million+ Add-ons used everyday

2000+ users signup everyday

WebExtensions

A cross-browser system for developing browser add-ons

Uses standard HTML, CSS and JS
e10s compatible (multiprocess)
Few changes and you can run it on Chrome, Edge and Opera
Documentations from multiple resources.

Why WebExtensions?

http://arewewebextensionsyet.com

Few WebExtension API's

alarms
bookmarks
tabs
storage
sidebarAction
contextMenus
webRequest
notifications

Anatomy/Architecture of WebExtensions

manifest.json

{
  "manifest_version": 2,
  "name": "inShorts in dark",
  "version": "2.0.1",
  "homepage_url": "https://github.com/viswanathamsantosh/inshorts",
  "description": "Read your favourite news on inShorts by dimming the light right away on your browser.",
  "icons": {
    "48": "icons/icon-48.png",
    "96": "icons/icon-96.png"
  },
  "permissions": [
    "activeTab",
    "tabs"
  ],
  "browser_action": {
  "browser_style": true,
  "default_icon": {
    "19": "icons/icon-19.png",
    "38": "icons/icon-38.png"
  },
  "default_title": "Turn on or off"
  },
  "background": {
    "scripts": ["background.js"]
  }
}

Background scripts

Loaded as soon as the extension is loaded
Stay loaded until the extension is disabled or uninstalled
You can use any of the WebExtension APIs in the script

"background": {
  "scripts": ["background-script.js"]
}

Content Scripts

Similar to loading normal scripts in the page
Can access DOM structure and use a small subset of the WebExtension APIs
Make cross-domain XHR requests
Exchange messages with their background scripts and can in this way indirectly access all the WebExtension APIs

"content_scripts": [
  {
    "matches": ["*://*.mozilla.org/*"],
    "js": ["jquery.js", "content-script.js"]
  }
]

Browser action

Used to add button to browser toolbar
Use this when your add-on's features are applicable to all websites else use Page action instead.

"browser_action": {
  "default_icon": {
    "19": "button/geo-19.png",
    "38": "button/geo-38.png"
  },
  "default_title": "Whereami?",
  "default_popup": "popup/choose_beast.html"
}

browser.browserAction.onClicked.addListener(handleClick);

Page action

Used to add button to address toolbar
Use this when your add-on's features are specific to a particular website.

"page_action": {
  "default_icon": {
    "19": "button/geo-19.png",
    "38": "button/geo-38.png"
  },
  "default_title": "Whereami?",
  "default_popup": "popup/choose_beast.html"
}

browser.pageAction.onClicked.addListener(handleClick);

Web-accessible resources

Resources such as images, HTML, CSS, and JavaScript that you include in the extension.

Developing your first browser add-on

Adding a browser action
Adding a page action
Accessing DOM from content scripts
Using a couple of WebExtension API's
Debugging your add-on

Debugging your add-on

Publishing your Add-on

https://addons.mozilla.org/en-US/developers/

Need help?

IRC Channels: #webextensions, #extdev, #addons

Mailing List: https://mail.mozilla.org/listinfo/dev-addons

Telegram: @addonschat

Questions?

Karthickeyan Narasimhan | @hellokarthic | mail@karthic.in

Slides: https://slides.com/hellokarthic/fx-addons

Building a cross browser extension with JS

By Karthickeyan Narasimhan

Building a cross browser extension with JS

Karthickeyan Narasimhan

Lead Software Engineer @ Freshworks