Enabling a simple form of Named Parameters in JavaScript A function that receives another function and returns a new function where Named Parameters have been enabled. It has been updated so that a function accepts both unnamed and named parameters. Notice the Named parameters must be passed as the last ones.

enableNamedParameters.js

//gets an array with the names of the parameters to a function
//taken from:
//http://stackoverflow.com/questions/9091838/get-function-parameter-names-for-interface-purposes/9092085#9092085
function getFnParamNames(fn){
    var fstr = fn.toString();
    return fstr.match(/\(.*?\)/)[0].replace(/[()]/gi,'').replace(/\s/gi,'').split(',');
}

//used to mark as such the support objects used to pass named parameters
function NamedParameters(obj){
	obj._isNamedParams = true;	
	return obj;
}

//returns a new function that enables a form of Named Parameters in the function passed as parameter
//based on how named parameters work in C#, we can pass a mix of named and unnamed parameters, but the Named ones must be passed over as the last ones
function enableNamedParameters(fn){
	if(typeof fn != "function")
		throw new Error("fn is not a function");
	if(fn._isNamedParamsEnabled || fn.length === 0){
		console.log(fn.name + " is already NamedParamsEnabled");	
		return fn;
	}
	var paramNames = getFnParamNames(fn);
	var namedParamsEnabledFn = function(){
		var params = [];
		//traverse the parameters that we've received, cheking if it's a normal one or a NamedParameter object. if present, the NamedParameter should be the last parameter provided, so other parameters after it are ignored
		for(var i=0; i<arguments.length; i++){
			if(!(arguments[i]._isNamedParams)){
				params.push(arguments[i]);
			}
			else{
				var paramsObj = arguments[i];
				for(;i<paramNames.length;i++){
					params.push(paramsObj[paramNames[i]]);
				}
				break;
			}
		}
		return fn.apply(this, params);
	};
	namedParamsEnabledFn._isNamedParamsEnabled = true; //metadata to avoid further applying of enableNamedParams
	return namedParamsEnabledFn;
}

if (typeof module !== "undefined" && module.exports){
	exports.enableNamedParameters = enableNamedParameters;
	exports.NamedParameters = NamedParameters;
}

test2.js

var np = require("./namedParameters2");
var enableNamedParameters = np.enableNamedParameters;
var NamedParameters = np.NamedParameters;

function sayHi(name, age, city, language){
	console.log("hi, my name is: " + name 
	+ " my age is: " + age
	+ " I live in: " + city
	+ " and my native language is: " + language);
}

var sayHi2 = enableNamedParameters(sayHi);

console.log("\n- using named parameters: ");
sayHi2(NamedParameters({
	city: "Prague",	
	age: 20,
	name: "Iyan"
	}
));

console.log("\n- using unnamed parameters: ");
sayHi2("Iyan", 20, "Prague", "English");

sayHi2("Iyan");

console.log("\n- using both unnamed and named parameters:");
sayHi2("Iyan", NamedParameters({
	language: "English",
	age: 20,
	city: "Prague"
}));

//notice the unnamed parameter "Prague" is being passed after the named ones, so it's being ignored
sayHi2("Iyan", NamedParameters({
	language: "English",
	age: 20}),
	"Prague"
);

//try to enable named params in a function where it's already enabled
var sayHi3 = enableNamedParameters(sayHi2);
console.log("just the same function was returned? " + (sayHi3 === sayHi2));