Unstable
API for working with the application observer service.
Usage
The system/events module provides core (low level) API for working with the application observer service, also known as nsIObserverService. You can find a list of events dispatched by the Firefox codebase here.
var events = require("sdk/system/events");
var { Ci } = require("chrome");
function listener(event) {
var channel = event.subject.QueryInterface(Ci.nsIHttpChannel);
channel.setRequestHeader("User-Agent", "MyBrowser/1.0", false);
}
events.on("http-on-modify-request", listener);
Globals
Functions
emit(type, event)
Send an event to observer service
Parameters
type : string
The event type.
event : object
An optional object with data and subject attributes. data refers to a string that you would like to pass through this event. subject should refer to the actual actor/subject of this event (ie: the object emitting the event).
on(type, listener, strong)
Listen to events of a given type
Parameters
type : string
The event type name to watch.
listener : function
Function that will be called when an event is fired, with a single event object as argument. This object has three attributes:
- type: the event type name
- subject: the event subject object
- data: the event data string
strong : boolean
Default is false, a weak reference, which means it can be garbage collected at any time if there are no other references to it. Determines if we should keep a strong or weak reference to the listener method.
once(type, listener, strong)
Listen only once to a particular event type
Parameters
type : string
The event type name to watch.
listener : function
Function that will be called when an event is fired.
strong : boolean
Default is false, a weak reference, which means it can be garbage collected at any time if there are no other references to it. Determines if we should keep a strong or weak reference to the listener method.
off(type, listener)
Stop listening for an event
Parameters
type : string
The event type name to unsubscribe to.
listener : function
The function we registered to listen for events.