An experiment to create named parameters in Javascript

gistfile1.txt

var reservedWords = "arguments caller length name prototype __proto__".split(" ")

module.exports = createNamedParameters

function createNamedParameters(argv, fn) {
	var length = fn.length
	var composed = Array(length)
	if (argv.length !== length) throw new Error("Argument lengths don't match")

	function composing() {
		var len = arguments.length, args = new Array(len)
		for (var i = 0; i < len; i++) args[i] = arguments[i]

		return applyFn(fn, composed.concat(args), this);
	}

	for (var i = 0; i < length; i++)
		addNamedParam(composing, composed, argv[i], i)

	return composing;
}

// Check that we're not modifying the function prototype with a reserved word
function addNamedParam(fn, args, name, pos) {
	if (~reservedWords.indexOf(name))
		throw new Error("Can't create named parameter with reserved word: " + name)

	fn[name] = function curryParam(v) {
		args[pos] = v
		return fn;
	}
}

// Make it fast for common cases
function applyFn(fn, args, ctx) {
	switch (args.length) {
		case 0: return fn.call(ctx); break;
		case 1: return fn.call(ctx, args[0]); break;
		case 2: return fn.call(ctx, args[0], args[1]); break;
		case 3: return fn.call(ctx, args[0], args[1], args[2]); break;
		default: return fn.apply(ctx, args);
	}
}

zzz.js

var create = require("./named-parameters")

var fn = create(["greeting", "person"], function(a, b) {
	console.log(a, b)
})

fn.greeting("hello").person("world")()