How do I make this. work with promises and generic functions

Question

I am trying to do something rather like the following:

function newCounter(){
    return {
        "counter" : 0
        ,"mode" : "new"
        ,"start" : function( arg_function ){
            //    Run this before counting.
            this.counter = 0;
            this.mode = "count";
        }
        ,"finished" : function(){
            // Run this when counting is no longer allowed.
            this.mode = "done";
        }
        ,"increment" : function(arg_key){
            globalThing.isValid(arg_key)
            .done(function(data){
                if( this.mode === "count" ){
                    this.counter++;
                }
            });
        }
    }
}

Now, the problem here, as one may notice, is that inside the .done() section there, I have a reference to this. - which does not and cannot refer to the object in question because it's inside a promise with a generic function, and as such, refers to window. and not the specific object being referenced from. I have tried these:

.done(function(data){
    if( this.mode === "count" ){
        this.counter++;
    }
}.apply(this))

.done(function(data){
    if( this.mode === "count" ){
        this.counter++;
    }
}.call(this))

as solutions, but they have not succeeded. I'm not entirely sure why. If you can see what I'm trying to do here ... could you recommend, please, a solution to my woes?

@bergi - could you reference where it is already answered? I'm not finding it, and I've been hunting for it. — Wolfman Joe, Sep 24 '15 at 18:15
@bergi This is not a duplicate of that question. The problem may be the same, but the contexts of the questions are different. — taxicala, Sep 24 '15 at 18:17
@taxicala: So then a duplicate of the generic [How to access the correct `this` / context inside a callback?](http://stackoverflow.com/q/20279484/1048572)? — Bergi, Sep 24 '15 at 21:59

score 2 · Accepted Answer · answered Sep 24 '15 at 18:06

2

Use bind instead:

.done(function(data){
    if( this.mode === "count" ){
        this.counter++;
    }
}.bind(this))

answered Sep 24 '15 at 18:06

taxicala

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No problem, glad to help. :) – taxicala Sep 24 '15 at 18:15

score 0 · Answer 2 · answered Sep 24 '15 at 18:07

You can always keep a reference to the object before returning it:

function newCounter(){
    var o = {
        "counter" : 0
        ,"mode" : "new"
        ,"start" : function( arg_function ){
            //    Run this before counting.
            o.counter = 0;
            o.mode = "count";
        }
        ,"finished" : function(){
            // Run this when counting is no longer allowed.
            o.mode = "done";
        }
        ,"increment" : function(arg_key){
            globalThing.isValid(arg_key)
            .done(function(data){
                if( o.mode === "count" ){
                    o.counter++;
                }
            });
        }
    }

    return o;
}

How do I make this. work with promises and generic functions

2 Answers2