Projectionist

Splat function arguments in JavaScript with Prototype 1.6.0

Object.extend(Function.prototype, (function() {
  function splat(args, index) {
    var result = new Array(index);
    for (var i = 0; i < index; i++)
      result[i] = args.shift();
    return result.concat([args]);
  }

  return {
    splatterize: function() {
      var names = this.argumentNames();
      if (names.last() != "$args") return this;

      return this.wrap(function() {
        var a = $A(arguments), orig = a.shift();
        return orig.apply(null, 
          splat(a, names.length - 1));
      });
    }
  };
})());


var x = (function(a, b, $args) {
  return { a: a, b: b, $args: $args };
}).splatterize();

// x(1)          => { a: 1, $args: [] }
// x(1, 2)       => { a: 1, b: 2, $args: [] }
// x(1, 2, 3)    => { a: 1, b: 2, $args: [3] }
// x(1, 2, 3, 4) => { a: 1, b: 2, $args: [3, 4] }