Create instance without `new` operator with variable argument list

Question

I want to create an instance of a Point with and without the new operator like:

Point(5, 10); // returns { x: 5, y: 10 }
// or
new Point(5, 10); // also returns { x: 5, y: 10 }

I got it working so far with the help of StackOverflow.

function Point() {
  if (!(this instanceof Point)) {
    var args = Array.prototype.slice.call(arguments);
    // bring in the context, needed for apply
    args.unshift(null);
    return new (Point.bind.apply(Point, args));
  }
  // determine X and Y values
  var pos = XY(Array.prototype.slice.call(arguments));
  this.x = pos.x;
  this.y = pos.y;
}

But that looks horrible, I am even unshifting null into the array so I can use apply. That just doesn't feel right.

I found a lot of solutions how to achieve it with new constructors and constructor wrappers but I want to keep it as simple as possible (it's just a plain, simple Point).

Is there an easier way to achieve this behaviour?

Answer 1

If you don't mind using ECMAScript 5 functions, Object.create() could help:

function Point()
{   var args = Array.prototype.slice.call(arguments);
    if (this instanceof Point) return Point.apply(null, args);
    var pos = XY(args); 
    var result = Object.create(Point.prototype);
    result.x = pos.x;
    result.y = pos.y;
    return result;
}

If you need ECMAScript 3 compatibility, this crazy, convoluted solution is yet another one (note that it's just a wrapper for an internal equivalent of new Point):

function Point() 
{   var pos = XY(Array.prototype.slice.call(arguments));
    function internalPoint()
    {   this.x = pos.x;
        this.y = pos.y;
    }
    internalPoint.prototype = Point.prototype;
    return new internalPoint;
}