This module is used in the internal implementation of SDK modules which use [content scripts to interact with web content](dev-guide/guides/content-scripts/index.html), such as the [`tabs`](modules/sdk/tabs.html), [`panel`](modules/sdk/panel.html), or [`page-mod`](modules/sdk/page-mod.html) modules. It exports the `Worker` trait, which enables content scripts and the add-on code to exchange messages using the [`port`](dev-guide/guides/content-scripts/using-port.html) or [`postMessage`](dev-guide/guides/content-scripts/using-postmessage.html) APIs. The `Worker` is similar to the [web worker][] interface defined by the W3C. But unlike "web workers," these workers run in the same process as web content and browser chrome, so code within workers can block the UI. [web worker]:http://www.w3.org/TR/workers/#worker @class Worker is composed from the [EventEmitter][] trait, therefore instances of Worker and their descendants expose all the public properties exposed by [EventEmitter][] along with additional public properties that are listed below. **Example** var workers = require("sdk/content/worker"); let worker = workers.Worker({ window: require("sdk/window/utils").getMostRecentBrowserWindow(), contentScript: "self.port.on('hello', function(name) { " + " self.port.emit('response', window.location.href); " + "});" }); worker.port.emit("hello", { name: "worker"}); worker.port.on("response", function (location) { console.log(location); }); [EventEmitter]:modules/sdk/deprecated/events.html @constructor Creates a content worker. @param options {object} Options for the constructor, with the following keys: @prop window {object} The content window to create JavaScript sandbox for communication with. @prop [contentScriptFile] {string,array} The local file URLs of content scripts to load. Content scripts specified by this option are loaded *before* those specified by the `contentScript` option. Optional. @prop [contentScript] {string,array} The texts of content scripts to load. Content scripts specified by this option are loaded *after* those specified by the `contentScriptFile` option. Optional. @prop [onMessage] {function} Functions that will registered as a listener to a 'message' events. @prop [onError] {function} Functions that will registered as a listener to an 'error' events. @property {EventEmitter} [EventEmitter](modules/sdk/deprecated/events.html) object that allows you to: * send customized messages to the worker using the `port.emit` function * receive events from the worker using the `port.on` function @method Asynchronously emits `"message"` events in the enclosed worker, where content script was loaded. @param data {number,string,JSON} The data to send. Must be stringifiable to JSON. @method Destroy the worker by removing the content script from the page and removing all registered listeners. A `detach` event is fired just before removal. @property {string} The URL of the content. @property {object} If this worker is attached to a content document, returns the related [tab](modules/sdk/tabs.html). @event This event allows the content worker to receive messages from its associated content scripts. Calling the `self.postMessage()` function from a content script will asynchronously emit the `message` event on the corresponding worker. @argument {value} The event listener is passed the message, which must be a JSON-serializable value. @event This event allows the content worker to react to an uncaught runtime script error that occurs in one of the content scripts. @argument {Error} The event listener is passed a single argument which is an [Error](https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Error) object. @event This event is emitted when the document associated with this worker is unloaded or the worker's `destroy()` method is called. Note that you can't communicate with the content script in response to this event. If you try, you'll see this error:

Error: Couldn't find the worker to receive this message.
The script may not be initialized yet, or may already have been unloaded

You can handle the `detach` event in the content script itself though: // in content script self.on("detach", function() { window.close(); });