JavaScript overloading with a callback

Question

Following the pattern recommended in this question, where we have something akin to:

function foo(a, b, opts) {

}

foo(1, 2, {"method":"add"});
foo(3, 4, {"test":"equals", "bar":"tree"});

How would one then include a callback as the final parameter? I have function foo() that should be able to handle both of:

foo(x, y, function() {
  // do stuff
});

And

foo(x, y, z, function() {
  // do stuff
});

Any suggestions?

Maybe I'm misreading or misunderstanding but are you asking if you can put a function within an object? — Snuffleupagus, Mar 22 '12 at 21:47
It is indeed possible. `{"oscar" : function () { console.log("I live in a trashcan.") }}` So, assuming you named your object foo, foo.oscar would run the function. — Snuffleupagus, Mar 26 '12 at 13:19

MiniGod · Answer 1 · 2013-02-12T04:37:18.090

1

You could do similar to .apply. (unlike .call)

function foo(args, cb) {}

foo(['a', 'b', 'c'], function() {} );

And if you need to, you could put them into variables using .shift:

function foo(args, cb) {
    var a = args.shift(),
        b = args.shift();
    // and so on...
}

edited Feb 12 '13 at 04:37

answered Feb 12 '13 at 04:29

MiniGod

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Paul · Answer 2 · 2012-03-22T22:04:46.767

1

I'd say just use the arguments object:

function foo(a, b) {
    // Do stuff


    // Done stuff


    var alength = arguments.length;

    // If more than 2 arguments and last argument is a function
    if(alength > 2 && typeof arguments[alength - 1] === 'function')
        arguments[alength - 1].call(this);
}

edited Mar 22 '12 at 22:04

answered Mar 22 '12 at 21:50

Paul

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but why do you use window.arguments instead of the local arguments variable? – Bergi Mar 22 '12 at 21:58

score 1 · Answer 3 · answered Mar 22 '12 at 21:51

1

So basically you want to accept a variable number of arguments, followed by a callback as the last one? Something similar to how PHP's array_udiff works?

This is fairly simple:

function foo() {
    var args = [], l = arguments.length, i;
    for( i=0; i<l; i++) args[i] = arguments[i];

    var callback = args.pop();
    // now you have your variable number of arguments as an array `args`
    // and your callback that was the last parameter.
}

answered Mar 22 '12 at 21:51

Niet the Dark Absol

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Why exactly would you create an exact copy of arguments array by `for` loop and then pop the callback, instead of just using `arguments`? – joncys Mar 22 '12 at 21:55
1

Because `arguments` is an array-like object, not an actual array. – Niet the Dark Absol Mar 22 '12 at 22:01
You could just use `var args = Array.prototype.slice.call(arguments)` – evan.bovie Dec 11 '13 at 01:49
@evan.bovie Could, but not allowed in older browsers ;) – Niet the Dark Absol Dec 11 '13 at 12:11
@NiettheDarkAbsol and that's when we drop support or use a shim. – evan.bovie Dec 16 '13 at 13:55
@evan.bovie And that is why I have a `for` loop ^_^ – Niet the Dark Absol Dec 16 '13 at 14:01

Unpossible · Accepted Answer · 2012-03-26T18:07:36.233

Ended up going with the following solution:

foo(args) {}

foo({"x":"add", "callback": function() {
  // do stuff
}});


foo({"x":"equals", "y":"tree", "callback": function() {
  // do stuff
}});

And then simply checking to see if the last arguments value is a function, ala @PaulP.R.O.'s solution above:

if((arguments.length > 1) && (typeof arguments[arguments.length - 1] === 'function')) {
  var callback = arguments[arguments.length - 1];
}

JavaScript overloading with a callback

4 Answers4

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