What's the best way to add a callback to the following module?

Question

I have the following module

var m=(function() {
   // setup variables

   return {
      center: function() {
        // do stuff
      },

      open: function(settings) {

        // do open stuff
        // setups the handler for the close...

            $close.on("click",function(e) {
               e.preventDefault();
               m.close();
            });
      },

      close: function() {
         // do close stuff
         // ** need to add code here 
         //to perform a callback function on close

         // EDIT
         if(this.hasOwnProperty("callback"))
            callback();
      },

      //** EDITED
      addCallback: function(func) {
         this.callback=func;
      }

   };
}());

// open 
m.open();

The close in the triggered automatically by a click event. I want to somehow insert a callback into the close() to be performed at the time of closing... I thought about adding a function like

addCallback(callback) { 
this.callback=callback;
}

but i'm not sure how to call that within the close().

** EDIT **

Thanks to user3297291 for the below response and Barmar you were right I do actually only need one callback not an array. I have edited the above code by adding a addCallback(). Then the code to run would be:

m.open()
function check() { 
   alert("hello");
}

m.addCallback(check);

But this doesn't work I'm trying to understand why and I new to javascript OO..

Answer 1

You'll have to keep track of an array of callbacks (or just one). The simplest implementation could be something like this:

 var m = (function() { var onCloseCallbacks = []; return { addOnCloseCallback: function(cb) { onCloseCallbacks.push(cb); }, close: function() { console.log("Closing"); onCloseCallbacks.forEach(function(cb) { cb(); }); } }; }()); m.addOnCloseCallback(function() { console.log("After close"); }); m.close(); 

Note that the array of callbacks is defined inside the closure.

For a more advanced solution, you'd want to be able to dispose the callback from outside of the m module. Here's an example of how this could be added:

 var m = (function() { var onCloseCallbacks = []; return { addOnCloseCallback: function(cb) { onCloseCallbacks.push(cb); return { dispose: function() { var i = onCloseCallbacks.indexOf(cb); onCloseCallbacks = onCloseCallbacks .slice(0, i) .concat(onCloseCallbacks.slice(i + 1)); } }; }, close: function() { console.log("Closing"); onCloseCallbacks.forEach(function(cb) { cb(); }); } }; }()); var myCallback = m.addOnCloseCallback(function() { console.log("After close"); }); m.close(); // Does trigger cb myCallback.dispose(); m.close(); // Doesn't trigger cb