Chrome extensions
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This document summarizes the key aspects of Chrome extensions including: - Chrome extensions are small programs that modify and enhance the Chrome browser functionality - Extensions have a general structure including manifest.json, background pages, content scripts, and CSS/HTML/JS files - Content scripts run in the context of web pages and have limited access to the Chrome API and web page resources - Extensions use message passing to communicate between the background page and content scripts
Chrome extensions
- 1. Oleksandr Zinevych Software Engineer at Datamart inc. Chrome Extensions
- 2. ▪ What is Chrome Extensions ▪ Common Architecture ▪ How all parts connects together ▪ Chrome Javascript API’s ▪ Known issues, and possible workarounds Agenda
- 3. What is chrome extension? Extensions are small software programs that can modify and enhance the functionality of the Chrome browser. Chrome Extension (.crx) CSS JS HTM L
- 4. General structure of chrome extension
- 6. Background/Event pages Background page, an invisible page that holds the main logic of the extension
- 7. Content scripts Content 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
- 8. ▪ 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)
- 9. Chrome Javascript API’s Chrome API’s Notifications Tabs History Downloads GCM …
- 10. Basic communication Google Chrome browser Background Page Tab Content Script ?
- 11. Message Passing Simple one-time requests
- 13. Content Scripts - Sandbox Content Scripts Web Page DOM JS
- 14. 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
- 15. Chrome extension architecture Browser Background Page Tab Web Page Content Script Web accessible resources DOM
- 16. Access to current web page scope Content Scripts Web Accessible Recourses Web Page Content Scripts web_accessible_recourses
- 17. Chrome extension architecture Browser Background Page Tab Web Page Content Script Web accessible resources Javascript DOM
- 18. Tips and tricks
- 19. 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
- 20. Pre-render Google Chrome browser Some text typed Item 1 Item 2 Item 3 Item 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:
- 21. 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
- 22. 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.
- 23. Access clipboard data Background Page
- 24. 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"
- 25. 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
- 26. Highlighting – the only one available way of tab visual editing. Both makes the tab active, and immediately switch to it. Tab visual appearance
- 27. 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
- 28. NPAPI Plugins(Deprecated) You can bundle an NPAPI plugin with your extension, allowing you to call into native binary code from JavaScript.
- 29. 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
- 30. Pros: ▪ Easy and fast develop ▪ Good for small functionality Cons: ▪ Scopes, Scopes, Scopes!!!! ▪ Limited and asynchronous API’s ▪ Security limitations Conclusion
- 31. Thanks!