splatify.js: Add some venom to your coffee

splatify.js

function splatify(func) {
	args_string = func.toString().split('(')[1].split(')')[0].split(',').map(function(s) { return s.trim(); });
	
	if (args_string.length && args_string[args_string.length - 1] === 'splat_args') {
		pivot = args_string.length - 1;
		
		return function () {
			if (arguments.length > pivot + 1) {
				args = Array.prototype.slice.call(arguments, 0, pivot);
				args.push(Array.prototype.slice.call(arguments, pivot));
				
				return func.apply(this, args);
			} else {
				args = Array.prototype.slice.call(arguments);
				for (i=args.length; i < pivot; i++) { args.push(undefined); }
				args.push([]);
				
				return func.apply(this, args);
			}
		}
	} else {
		return func;
	}
}

usage.js

// The usage is "DO NOT"
t = splatify(function t(foo, bar, splat_args) {
	console.log("foo=" + foo + ", bar=" + bar + ", splat_args=[" + splat_args.toString() + "]");
});

t(1) // foo=1, bar=undefined, splat_args=[]
t(1, 2) // foo=1, bar=2, splat_args=[]
t(1, 2, 3) // foo=1, bar=2, splat_args=[3]
t(1, 2, 3, 4) // foo=1, bar=2, splat_args=[3, 4]

Because, as per usual, IE lets us down.