Worker

Table of contents

  1. 1. Method overview
  2. 2. Properties
    1. 2.1. The error message
  3. 3. Methods
    1. 3.1. postMessage()
    2. 3.2. terminate()
  4. 4. See also
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« Gecko DOM Reference

Workers are background tasks that can be easily created and can send messages back to their creators. Creating a worker is as simple as calling the Worker() constructor, specifying a script to be run in the worker thread.

Of note is the fact that workers may in turn spawn new workers as long as those workers are hosted within the same origin as the parent page.  In addition, workers may use XMLHttpRequest for network I/O, with the exception that the responseXML and channel attributes on XMLHttpRequest always return null.

For a list of global functions available to workers, see Functions available to workers.

Gecko 2.0 note
(Firefox 4 / Thunderbird 3.3 / SeaMonkey 2.1)

If you want to use workers in extensions, and would like to have access to js-ctypes, you should use the ChromeWorker object instead.

See Using web workers for examples and details.

Method overview

void postMessage(in JSObject message);
void terminate();

Properties

Property Type Description
onmessage EventListener An event listener that is called whenever a MessageEvent with type message bubbles through the worker. The message is stored in the event's data member.
onerror EventListener An event listener that is called whenever an ErrorEvent with type error bubbles through the worker.

The error message

The error message contains three properties:

message
A human-readable error message.
filename
The name of the script file in which the error occurred.
lineno
The line number of the script file on which the error occurred.

Methods

postMessage()

Sends a message to the worker's inner scope. This accepts a single parameter, which is the data to send to the worker. The data may be any value or JavaScript object that does not contain functions or cyclical references (since the object is converted to JSON internally).

void postMessage(
  in JSObject aMessage
);
Parameters
aMessage
The object to deliver to the worker; this will be in the data field in the event delivered to the onmessage handler. This may be any value or JavaScript object that does not contain functions or cyclical references (since the object is converted to JSON internally).

terminate()

Immediately terminates the worker. This does not offer the worker an opportunity to finish its operations; it is simply stopped at once.

void terminate();
Parameters

None.

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