How do I add “onload” to my Dojo class?

Question

I'd like to add an "onload" function to my custom Dojo class such that it can call functions that register to for the event - something like myWidget.addOnLoad(...)

My class is not a Dijit it's a simple class that uses dojo.declare. Upon creation several functions are called (xhr, etc) to initialize the class and I need the ability to notify other javascript functions that the widget is loaded & ready.

Answer 1

As jburke already pointed out Dojo makes it easy for you: dojo.connect is all you need. Here's an example:

a = {
    loaded: function() { console.log('[a] loaded'); }
}
b = {
    dependentAction: function() { console.log('[b] dependentAction'); }
}
dojo.connect( a, 'loaded', b, 'dependentAction' );
a.loaded()
// prints:
// [a] loaded
// [b] dependentAction

And then just execute a.loaded() after you're done with loading a.

Answer 2

Have you considered using dojo.publish() to publish a topic when the widget is ready? Or, if the other code has a reference to the widget, you can call an empty function on the widget instance when your widget is loaded (call it "loaded"), and then the other code that has a reference to the instance can dojo.connect to that widget instance's "loaded" method to get notified when the method is called.

Answer 3

So I went ahead & basically copied the Dojo addOnLoad functions & added it to my class. It seems to be working. I looked at doing a pub/sub or a dojo.connect, but I feel like this was the cleanest, most recognizable solution.

Below are the necessary bits to get it going, again stripped out of dojo.js and plugged into my class:

_onto : function(arr, obj, fn){
    if(!fn){
        arr.push(obj);
    }else if(fn){
        var func = (typeof fn == "string") ? obj[fn] : fn;
        arr.push(function(){ func.call(obj); });
    }
},

_loaded : function() {
    this._loadNotifying = true;
    this._postLoad = true;
    var mll = this._loaders;
    for(var x = 0; x < mll.length; x++){
        try{
            mll[x]();
        }catch(e){
            throw e;
            console.error("addOnLoad callback failed: " + e, e); /* let other load events fire, like the parser, but report the error */
        }
    }
    this._loadNotifying = false;
    //Make sure nothing else got added to the onload queue
    //after this first run. If something did, and we are not waiting for any
    //more inflight resources, run again.
    if(this._postLoad && this._inFlightCount == 0 && mll.length){
        this._loaded();
    }
},

addOnLoad : function(/*Object?*/obj, /*String|Function?*/functionName){
    this._onto(this._loaders, obj, functionName);   
    if(this._postLoad && !this._loadNotifying){
        this._loaded();
    }
}