如何在firefox插件中只运行一个代码实例？

Question

I listen for a onload event on a main window, then for a DOMContentLoaded event on each browser/tab (I need run the code inside a browser at the most) and flag with controlExecuted that the code was run on a browser.

window.addEventListener("load", function(){
    try{
        var controlExecuted = 0;
        var appcontent = document.getElementById("appcontent"); // browser
        if (appcontent && controlExecuted == 0)
            appcontent.addEventListener("DOMContentLoaded", function docLoader(e){
                appcontent.removeEventListener("DOMContentLoaded", docLoader, false);
                alert('run code')
                controlExecuted = 1;
            }, true);
    }catch(e){
        // log!
    }
}, false);

This not works. The code run several times depending of the number of browsers/tabs.

So how to run only one instance of code in a firefox addon?

Answer 1

As you've noticed, your code runs each time a new browser window is opened. What you might not have realized is that a script in one window is completely independent of the same script in another window. That is, a new set of objects is instantiated each time, which means that controlExecuted in one window is not the same object as controlExecuted in another window.

There are two broad ways to share code in an extension:

• Create an XPCOM component . This is the classic, more difficult (but very powerful) method of sharing code in a browser extension.

• Create a JavaScript code module (JSM). In short:

  JavaScript code modules are a concept introduced in Gecko 1.9 and can be used for sharing code between different privileged scopes. Modules can also be used to create global JavaScript singletons that previously required using JavaScript XPCOM objects.

You might also consider setting this flag as a user preference , which each instance of your script can read. This might be the easiest approach for such a simple use case.

Answer 2

Here the complete solution to run only one instance of code in a firefox addon using JavaScript code modules .

// modules/main.jsm
var EXPORTED_SYMBOLS = ["instancesControl"];

var instancesControl = {
    executed : 0,
    windowExecuting : 0,

    get : function(){
        return ++instancesControl.executed;
    },
    reset : function(){
        instancesControl.executed = 0;
    },
    getWindowExecuting : function(){
        return instancesControl.windowExecuting;
    },
    setWindowExecuting : function(id){
        instancesControl.windowExecuting = id;
    }   
};

The main calling code:

 // load instancesControl module
Components.utils.import("resource://my-own-alias/main.jsm");

// identify window that will execute the one-instance code
var util = window.QueryInterface(Components.interfaces.nsIInterfaceRequestor)
.getInterface(Components.interfaces.nsIDOMWindowUtils);
var windowID = util.outerWindowID;

// listen load window event 
window.addEventListener("load", function(){
    var appcontent = document.getElementById("appcontent");
    if (appcontent){
        // listen load content (on every tab)
        appcontent.addEventListener("DOMContentLoaded", function docLoader(e){
            appcontent.removeEventListener("DOMContentLoaded", docLoader, false);
            if (instancesControl.get() == 1){
                instancesControl.setWindowExecuting(windowID);

                // this code will run only once no matter
                // how many tabs or windows user opens.

            }
        }, true);
    }
}, false);

// re-init code if executing windows is closed
window.addEventListener("unload", function(){
    if (instancesControl.getWindowExecuting() == windowID){
        instancesControl.reset();
    }
}, false);

Sure that you can improve it. Comment using @nomikos if you do.
THX.