Allow overloading of methods using arbitrary conditions, including shorcuts for artity.
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Allow overloading of methods using arbitrary conditions, including shorcuts for artity.


  • Methods are overloaded in a first-in-last-called manner. Newer functions take priority.
  • Only one function will ever be called per method. Returning true from a condition stops the chain.
  • Much of the functionality you see here was implemented using Overload. Use it on itself!
  • Overload will polyfill Function.prototype.bind (using overload._bind).


Overload uses a slightly custom version of the UMD pattern, and should work in almost any situation you put it in. It supports AMD (RequireJS, etc), CommonJS (Node) and browser globals.

To install it in the browser, copy one of the two files in the dist folder to your project, and simply include it on your page.

If you're using Node, you get to install overload using npm, which is as easy as pie!

npm install node-overload

You can also install overload using bower.

bower install overload


// Define our object
var Person = function() {}

// Set the default method. You could also do this
// just by setting it manually.
overload.add(Person.prototype, 'speak', true, function() {
    console.log('Peasant! Learn to call me correctly!')

// If we've only been passed one argument, say it
// You can also do this by omitting the number. It'll
// then take the amount of arguments the function takes
// and use that number instead
overload.add(Person.prototype, 'speak', 1, function(speech) {

// If we are passed an arguments saying "christmas", trigger
// an anti-fesive message
overload.add(Person.prototype, 'speak', function(method, args) {
    return, 'christmas') !== -1;
}, function() {
    console.log('Bah, humbug!');

// If we've been passed too many arguments, complain
overload.add(Person.prototype, 'speak', function(method, args) {
    return args.length > 1;
}, function() {
    console.log('I\'m too busy for this!');

var scrooge = new Person();

// Peasant! Learn to call me correctly!

// Bah, humbug!

// money

scrooge.speak('money', 'fame');
// I'm too busy for this!


One of the best uses for this would be to use it to have different functions for different "artities". You can do this quite easily with overload.

var Bike = function() {}; = function() {

overload.add(Bike.prototype, 'drive', function(person1, person2) {
    console.log('Too many people!');

var bike = new Bike();;
// Wahoo!'one', 'two');
// Too many people!

You can also do ranges of arity, so you can say if the method is passed two or more arguments, call a certain version of the method. This is done via the overload.arity method.

The syntax is like so:

var two_or_more = overload.arity(2);
var one_or_less = overload.arity(0, 1);

overload.add(obj, 'method', one_or_less, function() {
    // ...

overload.add(obj, 'method', two_or_more, function() {
    // ...

Getting a clean version of Overload

For whatever reason, you might want to extend your own shortcuts onto a clean version of Overload (the initial function before we overload it with shortcuts).

You can do this quite easily with the following.

var clean = overload.clean();