Javascript callback from namespace

Question

I have a namespace setup like this:

var myApp = {};
(function(context) {
    var id = 0;

    context.next = function() {
        return id++;
    };

    context.reset = function() {
        id = 0;
    }
})(myApp);
window.console && console.log(
    myApp.next(),
    myApp.next(),
    myApp.reset(),
    myApp.next()
) //0, 1, undefined, 0

I now want to to have a callback from myApp which i can catch outside of the namespace..

Any ideas how to set that up with my namespace setup?

For example something like this:

myApp.setCallback('next', function() {
    alert('hello');
 });

What do you mean by *"a callback from myApp which i can catch outside"*? — Joseph, May 11 '13 at 12:13
answered [something similar](http://stackoverflow.com/questions/16427077/add-function-to-object/) couple days ago ... — Tim Vermaelen, May 11 '13 at 12:14
I guess you would have to pass a callback to all the inner functions and check on that callback when the function executes, and then run it..(so you can either pass a callback or not) — vsync, May 11 '13 at 12:21
Perhaps you could use something like an "event"-pattern, so your app triggers the event "next", and every other object subscribed to this event could do something. — Thomas Junk, May 11 '13 at 12:23

score 3 · Accepted Answer · answered May 11 '13 at 12:20

3

You can test for the existance of a callback and run the function if it exists:

var myApp = {};

(function(context) {
    var id = 0;

    context.next = function() {
        return id++;
    };

    context.reset = function() {
        id = 0;

        if(typeof this.onreset === 'function') {
            this.onreset();
        }
    }
})(myApp);


myApp.onreset = function() {};

answered May 11 '13 at 12:20

Tom Elmore

1,980
15
20

This is a nice simple solution. – MarioDS May 11 '13 at 12:35

MarioDS · Answer 2 · 2013-05-11T14:38:42.237

You need to add an object containing the callback functions and a function to register them:

var myApp = {};
(function(context) {
    var id = 0;

    var callbacks = {};

    context.next = function() {
        id++;
        doCallbacks('next');
        return id;
    };

    context.setCallback = function(event, f) {
        if(!callbacks[event] || !callbacks[event] instanceof Array) {
            callbacks[event] = [];
        }
        callbacks[event].push(f);
    }

    context.reset = function() {
        id = 0;
    }

    function doCallbacks(key /*, event */) {
        if(callbacks[key] && callbacks[key] instanceof Array) {
            for(var i=0; i < callbacks[key].length; i++) {
                callbacks[key][i](/*event*/);
            }
        }
    }
})(myApp);

And then you can call:

myApp.setCallback('next', function() {
    alert('hello');
});

working jsFiddle

working jsFiddle with event objects

You may need to tweak the check for an array a bit though, I don't know how to do it perfectly.

Your `if` block in the `next` method never execute, because it is after `return` statement. — , May 11 '13 at 12:29

Javascript callback from namespace

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