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Keyword arguments for Javascript. Similar to python's kwargs

This little tool gives you the ability to use keyword arguments support for your functions. So you can either specify each argument as you wish or use the arguments regularly. In fact you can do both at the same time.

Another feature is to have the ability to set default values for your function arguments without changing or adding any code to your function.

Build Status


Just include the script on your site. That's it. When included it will add a new method called kwargs to Function prototype and you can use it like this:

var functionName = function(arg1, arg2){
    // code

With node.js

You can install it with npm

npm install kwargsjs

and include it on your scripts

var kwargs = require('kwargsjs');
var functionName = kwargs(function(arg1, arg2){
    // code
}, [defaults]);
// or using function prototype
var functionName = function(arg1, arg2){
    // code


Just write your function as you would normally, and don't worry about the arguments size. just call .kwargs() and rest will be handled.

var test = function(arg1, arg2, arg3){
    // Your code

Now, if you want you can pass all arguments in a single object and they all will be mapped to their correct places

    arg3: 'val3',
    arg1: 'val1',
    arg2: 'val2'

You can also use your function like you would normally use

test('val1', 'val2', 'val3');

the best part is that you can do both

test('val1', {
    arg3: 'val3',
    arg1: 'val1',

Using Default values for arguments

Let's say we have this function that says Hello to a given name.

var greeting = function(name){
    return "Hello " + name;
greeting('Frank'); // -> Hello Frank

If no name is given, we want it to return "Hello World", usually you would have to add conditions to your function and check for existence of name argument. kwargs automatically handles that for you.

var greeting = function(name){
    return "Hello " + name;
}.kwargs({name: 'World'}); // Set a default value for your argument and
                           // it will be used when this argument is empty
// Here are the results
greeting('Frank'); // -> Hello Frank
greeting(); // -> Hello World

A real example

Let's say we have a function that receives a lot of arguments and generates a name with prefixes and suffixes when provided.

var name = function(firstName, lastName, middleName, prefix, suffix){
    var name = [];
    return name.join(' ');

Now, when we want create a name with only a suffix, all we have to do is to provide the name and suffix. You can only pass required arguments without changing anything on your function code.

name('John', 'Doe', { suffix:'Ph.D.' });
// -> John Doe Ph.D.
name('Max', 'Fightmaster', { prefix: 'Staff Sgt.' })
// -> Staff Sgt. Max Fightmaster
name('Isaac', 'Newton', { prefix: 'Sir', suffix: 'PRS MP'});
// -> Sir Isaac Newton PRS MP


Name Mangling

Some javascript minifiers such as UglifyJS are using a technique called mangling which shortens the code by changing the argument and variable names in your function, this feature might break kwargs because it relies on these names. You can either disable this feature on your minifier or define your argument names as reserved words in mangle options

Kwargs argument and reguler object arguments

If last argument passed is an object, code assumes it's a kwargs object, if your function accepts objects as arguments you should be careful about this, here is an example.

// in both cases, `anObject` argument will be interpreted as `kwargs` object and be ignored
myFunc('val', anObject);

to avoid this problem you have two solutions

myFunc(anObject, {}); // passing last argument as an empty object
// or using the options method and passing your object in kwargs
  arg1: anObject


MIT License