executeScript() and executeCSS()

Problem

Sometimes, extension developers don't need to execute content script in a page until some event happens in the extension. It is wasteful to execute content script in every web page on the off chance that this event will happen.

For example, consider an extension that wants to translate web pages. There will be a button in the UI that enables translation. When this button is pressed, the DOM needs to be crawled, collecting text nodes, and concatenating them for translation. However, it would be nice to avoid running content scripts until this button is pressed.

Proposal

chrome.tabs

// Executes JavaScript in the root frame of a tab. The script is executed in the same type of

// sandbox that content scripts are.

//

// Each time this method is called a new sandbox is created to run the script and the sandbox

// persists following the usual rules of GC. This isn't particularly heavyweight, but it also

// isn't something you'd want to do in a loop.

//

// If you need lots of small communication with a tab, consider executing script once and

// then using content script messaging to communicate between that script and the extension.

//

// tabId: Optional, defaults to selected tab of the current window (as determined by

// chrome.windows.getCurrent()).

// js: Optional, string of JavaScript to execute.

// js_files: Optional, array of JavaScript files to execute, in order.

// callback: Optional, callback to invoke with result of execution (result of last statement).

//

// If the extension does not have access to interact with the URL in the specified tab, or if a

// js file is specified that does not exist, an error is reported to the console associated with the

// view that called the API. Execution errors in the script are reported to the console associated

// with the tab.

void executeScript([int tabId], {[string js], [string[] js_files]}, [callback onSuccess(Object result)]);

// Applies CSS to the root frame of a tab.

//

// tabId: Optional, defaults to selected tab of the current window (as determined by

// chrome.windows.getCurrent()).

// css: Optional, string of CSS to execute.

// css_files: Optional, array of CSS files to execute, in order.

void insertCSS([int tabId], {[string css], [string[] css_files]});

Example

chrome.tabs.executeScript(null, {js_files: ["jquery/min.js", "woo.js"]});

Details

• When we implement permissions, this API should fail if the extension doesn't have access to the page loaded into the tab.
• No attempt is made to dedupe these. Each time you call the API, the script gets executed again. Callers need to maintain state if they don't want to execute duplicate scripts.
• Executing script in subframes is not supported.