Convert arguments to Array

By  on  

The arguments object thats automatically available within functions can be a source of confusion for some people; it's kind of an array but it's kinda not. JavaScript is awesome in that you can pass any number of arguments to a function, and oftentimes developers need to iterate over every argument provided.  The arguments object doesn't have a forEach method, but using a quick JavaScript technique, you can convert arguments to an array:

function myFn(/* any number of arguments */) {
	var args = Array.prototype.slice.call(arguments);
		// or [].slice.call(arguments)

	args.forEach(function(arg) {
		// do something with args here
	});
}

Much like converting a NodeList to an array, Array's slice method takes the arguments object and converts it to a true array, allowing for forEach, map, and traditional array iteration.  Keep that trick up your sleeve for future development.

Recent Features

  • By
    How I Stopped WordPress Comment Spam

    I love almost every part of being a tech blogger:  learning, preaching, bantering, researching.  The one part about blogging that I absolutely loathe:  dealing with SPAM comments.  For the past two years, my blog has registered 8,000+ SPAM comments per day.  PER DAY.  Bloating my database...

  • By
    JavaScript Promise API

    While synchronous code is easier to follow and debug, async is generally better for performance and flexibility. Why "hold up the show" when you can trigger numerous requests at once and then handle them when each is ready?  Promises are becoming a big part of the JavaScript world...

Incredible Demos

  • By
    Introducing MooTools LazyLoad

    Once concept I'm very fond of is lazy loading. Lazy loading defers the loading of resources (usually images) until they are needed. Why load stuff you never need if you can prevent it, right? I've created LazyLoad, a customizable MooTools plugin that...

  • By
    Prevent Page Zooming in Mobile Browsers

    Ever since I got my iPhone, I've been more agreeable in going places that my fiancee wants to go. It's not because I have any interest in checking out women's shoes, looking at flowers, or that type of stuff -- it's because my iPhone lets...

Discussion

  1. If you’re using Firefox, or in the future when other browsers support ES6, you can do it more elegantly:

    function myFn(...args) {
      /* code */
    }
  2. In case you are using Mootools, Array.from does the job, isn’t it ?

  3. Dmitry Tsvettsikh

    Why not it:

    var args = Array.apply(null, arguments);
    
    • David

      You can do that but be aware if you do something like:

        function x(){
         return Array.apply(null, arguments);
        };
        x(10); //=> it will return empty array with a length of 10 instead of [10]
      
  4. islomjon

    Cool trick, but why even typeof arguments returns object?

  5. We have a new method, Array.from(arguments)

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!