prevent extension script from running multiple times using XPCOM observers Topic is solved

[BZZZZ]

EDIT: Don't do this! there are better ways.

Code: Select all

var observice=Components.classes["@mozilla.org/observer-service;1"].getService(Components.interfaces.nsIObserverService);
var anti_multi_observer_topic="{insert unique observer topic string}";
if(!observice.enumerateObservers(anti_multi_observer_topic).hasMoreElements()){
  observice.addObserver({},anti_multi_observer_topic,false);//this observer does nothing, it exists for if check above next time script runs
  //insert code to run only first time
}

Replace {insert unique observer topic string} with unique observer topic string.
Replace //insert code to run only first time with code to run only first time.

Use when you need to run something once in script that might run multiple times.
Example: <script> in chrome://browser/content/browser.xul overlay will run every time new browser window is opened.
Example: you need to add only one observer because observers are global for all browser windows in same process.

Links:

• XPCOM Interface Reference
• nsIObserverService

[moonbat]

If you don't want something to run multiple times, you put it in a Javascript module that gets loaded only once at browser startup. There's no need for complicated hacks like this.

[New Tobin Paradigm]

You mean an xpcom js component.

[Moonchild]

It's the wrong approach anyway. Observers are very heavy and will affect performance. You don't need them if you simply use a prototyped object for your code that holds a variable (e.g. _inited) and set/check that. Leverage the native JS paradigms.

[New Tobin Paradigm]

Since this "Tutorial" is in question, may I suggest it be moved to UXP Development or the Add-ons Board. In the future it MAY be wise to check with us before posting in here because of issues like this where the "Tutorial" is not advised or misguided.

To the topic, this is the basic way to build an XPCOM JS Component properly. What is suggested by the OP is frankly insane and should not be used.

http://udn.realityripple.com/docs/Mozilla/Tech/XPCOM/Guide/Building_components_in_JavaScript

Additionally, here is are a few functional example which I been using here and there based off older Adblock Plus code:

https://git.binaryoutcast.com/adblocker/src/branch/TRUNK/components/Initializer.js
https://git.binaryoutcast.com/inspector/src/branch/TRUNK/components/initializer.js
https://git.binaryoutcast.com/elemhidehelper/src/branch/TRUNK/components/initializer.js

[BZZZZ]

If you don't want something to run multiple times, you put it in a Javascript module that gets loaded only once at browser startup. There's no need for complicated hacks like this.

Thank you!

Script imported by Components.utils.import() run only when imported first time!

Can someone append "THIS IS BAD WAY OF DOING THIS!" to original post?

[moonbat]

I would recommend going through the XUL Tutorial, because even if you're familiar with Javascript, you still need to understand script interaction and how the browser uses them. This isn't a regular webpage script situation after all.