Oleksandr ZinevychSoftware Engineer at Datamart inc.

Chrome Extensions

▪What is Chrome Extensions▪Common Architecture▪How all parts connects together▪Chrome Javascript API’s▪Known issues, and possible workarounds

Agenda

What is chrome extension?

Extensions are small software programs that can modify and enhance the functionality of the Chrome browser. Chrome

Extension (.crx)

CSS

JSHTM

L

General structure of chrome extension

Example of manifest.json

Background/Event pagesBackground page, an invisible page that holds the main logic of the extension

Content scriptsContent scripts are JS files that run in the context of web pages.

▪Use limited chrome.* APIs▪Cannot use variables or

functions defined by their extension's pages▪Cannot use variables or

functions defined by web pages or by other content scripts

▪Eval and related functions are disabled▪Inline JavaScript will not be executed▪Only local script and and object resources are loaded

Content Security Policy (CSP)

Chrome Javascript API’s

Chrome API’s

Notifications

Tabs

History Downloads

GCM

…

Basic communicationGoogle Chrome browser

Background Page

Tab

Content Script ?

Message PassingSimple one-time

requests

Message PassingLong-lived connections

Content Scripts - Sandbox

Content Scripts

Web Page

DOM

JS

In manifest.json is an array of strings specifying the paths of packaged resources that are expected to be usable in the context of a web page.

web_accessible_recourses

Chrome extension architectureBrowser

Background Page

TabWeb Page

Content Script

Web accessible resources DOM

Access to current web page scope

Content Scripts

Web Accessibl

e Recourse

s

Web Page

Content Scripts

web_accessible_recourses

Chrome extension architectureBrowser

Background Page

TabWeb Page

Content Script

Web accessible resources

Javascript

DOM

Tips and tricks

This function becomes invalid when the event listener returns, unless you return true from the event listener to indicate you wish to send a response asynchronously (this will keep the message channel open to the other end until sendResponse is called).

Keep the message channel open

Pre-renderGoogle Chrome browserSome text typed

Item 1Item 2Item 3Item 4

….Item 8

Hidden Tab

When typing into the address bar, browser try to predict which links could be selected from the proposed list, and pre-render them into the hidden tab. It will replace the current tab, in case the appropriate list item will be clicked.

Hidden Tab Hidden Tab

Hidden Tab

Address Bar:

For performance reasons Chrome can spawn a separate, invisible tab, and swap an existing tab with this pre-rendered tab.

Tab Id – not a constant

Tab navigation delay

Background page

Tab

Content Scripts

1.

2.

3.

1. Send message, Content script made some activity which cause navigation, send response.2. Check if page load is complete or in progress, send response.3. Send message to Content Scripts. Here navigation started and request is broken.

Access clipboard data

Background Page

The history and webNavigation API’s uses a transition type to describe how the browser navigated to a particular URL. In addition, several transition qualifiers can be returned that further define the navigation.

Transition types and qualifiers

TransitionType: "link", "typed“, "auto_bookmark", "auto_subframe", "manual_subframe", "generated", "auto_toplevel", "form_submit","reload", "keyword", or "keyword_generated" TransitionQualifiers: "client_redirect", "server_redirect", "forward_back", or "from_address_bar"

History of specific tab is unavailable.

▪search - Searches the history for the last visit time of each page matching the query▪getVisits - Retrieves information about visits to a URL▪addUrl - Adds a URL to the history at the current time with a transition type of "link"▪deleteUrl - Removes all occurrences of the given URL▪deleteRange - Removes all items within the specified date range from the history▪deleteAll - Deletes all items from the history

History API

Highlighting – the only one available way of tab visual editing.

Both makes the tab active, and immediately switch to it.

Tab visual appearance

In chrome.windows API, during creation or updating some window, window State property can be one of the following options:

▪fullscreen in Mac OS – move window to the separate desktop.▪maximize in Mac OS – change window height to the

whole available height on screen.

Resizing

NPAPI Plugins(Deprecated)

 You can bundle an NPAPI plugin with your extension, allowing you to call into native binary code from JavaScript.

NaCL and PNaCl▪Native Client is a sandbox for running compiled C and C++

code in the browser efficiently and securely, independent of the user’s operating system▪Portable Native Client extends that technology with

architecture independence, letting developers compile their code once to run in any website and on any architecture

Pros:▪Easy and fast develop▪Good for small functionality

Cons:▪Scopes, Scopes, Scopes!!!!▪Limited and asynchronous API’s▪Security limitations

Conclusion

Thanks!