adding callback to function - always

Question

I found myself using a weird way to add callback functions to my functions and I was wondering if there is a more generic way to add callbacks to functions, best case I would have a situation where all of my functions check the last given param for being a function and if so use it as a callback.

This is how I did it in the past:

var myFunc = function( obj ) {

  if ( arguments.length > 0 ) {
    if ( _.util.typeofObj( arguments[arguments.length-1] ) === Function ) {
      var callback = arguments[arguments.length-1];
    }
  }

  // some code ...

  if ( callback !== undefined ) {
    callback();
  }

};

var foo = myFunc( myObj, function(){
  alert( 'Callback!' );
});

Any suggestions?

Vivin Paliath · Accepted Answer · 2011-03-28 20:14:40Z

13

I prefer a formal parameter:

var myFunc = function(obj, callback) {
   ...
}

This way it makes it obvious that there is a callback. You also don't have to mess around with the arguments object; you can just check to see if callback is undefined, and then check to see if it is of the appropriate type (Function).

answered Mar 28, 2011 at 20:14

Vivin Paliath

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3 Comments

ezmilhouse Over a year ago

after using the prototype solution for a few weeks now, I switched to your advice, it's just easier to read, find it to be a very important eyecatcher

Vivin Paliath Over a year ago

@ezmilhouse yes, there's less "magic" happening because the formal parameter is obvious :)

Vivin Paliath Over a year ago

@ezmilhouse I suggest changing the accepted answer since you mentioned that you changed your approach.

user578895 · Accepted Answer · 2011-03-28 20:15:20Z

5

You could, if you really want to, extend Function.prototype with a .cb prototype. Something like:

Function.prototype.cb = function(cb){
   var self = this;
   return function(){
      self.callback = cb || function(){};
      self.apply(self, arguments);
   }
}

then your code would compress to:

var myFunc = function(obj){
   // some code

   this.callback(); // callback will always be defined
}

and the call would slightly change:

myFunc.cb(function(){
   // callback code
})(myObj);

Just an idea. You can make the syntax pretty much whatever you want.

answered Mar 28, 2011 at 20:15

user578895

1 Comment

Shaz Over a year ago

In this case it might not matter much, however, might want to avoid using self since it's a global (yet not reserved) variable.

Justin Thomas · Accepted Answer · 2011-03-28 20:14:13Z

5

Not sure what you are trying to do here, but a way to add a callback that seems more straight forward:

function( obj, callback ) {
   if(callback) {
      callback();
   }
}

answered Mar 28, 2011 at 20:14

Justin Thomas

5,8473 gold badges44 silver badges63 bronze badges

2 Comments

Jacob Over a year ago

Or to cause some head-scratching, abbreviate as callback && callback()

Andrey Over a year ago

@Jackob: typeof callback == "function" && callback() is cleaner

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