Java-esque method overloading for JavaScript.

overloading.js

// Don't actually use this. Ever. Thx.

(function() {

  var getClass = {}.toString, slice = [].slice, classNames = {
    "[object Function]": "Function",
    "[object Array]": "Array",
    "[object String]": "String",
    "[object Boolean]": "Boolean",
    "[object Number]": "Number",
    "[object Date]": "Date",
    "[object RegExp]": "RegExp"
  };
  function getClassOf(value) {
    var className;
    if (value === null) {
      return "Null";
    } else if (value == null) {
      return "Undefined";
    }
    className = getClass.call(value);
    return classNames.hasOwnProperty(className) ? classNames[className] : "Object";
  }

  Function.overload = function(obj) {
    return function() {
      var signature = [], length = arguments.length;
      while (length--) signature[length] = getClassOf(arguments[length]);
      signature = signature.join(", ");
      if (obj[signature]) {
        return obj[signature].apply(this, arguments);
      } else {
        throw new Error('Signature "' + signature + '" not defined.');
      }
    };
  };
  
}());

usage.js

var func = Function.overload({
  'Number, String': function(n, s) {
    return 'The number ' + n + ' was passed, followed by string ' + s;
  },
  'String, Number': function(s, n) {
    return 'The string ' + s + ' was passed, followed by number ' + n;
  }
});

func(123, 'foo')  // "The number 123 was passed, followed by string foo"
func('foo', 123)  // "The string foo was passed, followed by number 123"
func(123, 456)    // Error: Signature "number, number" not defined.

This is cool as hell. 👏

Why isPropertyOf.call(classNames, className) instead of classNames.hasOwnProperty(className) ?

Also, this should probably handle Null and Undefined too :D

@cowboy isPropertyOf.call is an unfortunate habit acquired from using the toString, slice, and isPropertyOf boilerplate in nearly all my projects. 🐟 Thanks for catching that; I've updated the code to support Null and Undefined as well.

You could also do:

if (value === null) {
  return "Null";
} else if (value == null) {
  return "Undefined";
}

@cowboy Sure. I thought typeof value == "undefined" would have been more readable, but value == null is far shorter.

That's what well-thought-out comments are for!

Indeed! 🐟