Determining Object Type with MooTools’ typeOf

By  on  

One thing about JavaScript I dislike is the vagueness of what the typeof operator returns. Pass typeof an array? You get "object" back (which it is, but a more concise answer would be helpful). Pass typeof a Date object? You get "object" again. What if there was a better way of determining an object's descriptive type? That's where the typeOf function within MooTools Core comes into play.

typeOf Source and Usage

The typeOf function is actually quite short:

var typeOf = this.typeOf = function(item){
	if (item == null) return 'null';
	if (item.$family) return item.$family();

	if (item.nodeName){
		if (item.nodeType == 1) return 'element';
		if (item.nodeType == 3) return (/\S/).test(item.nodeValue) ? 'textnode' : 'whitespace';
	} else if (typeof item.length == 'number'){
		if (item.callee) return 'arguments';
		if ('item' in item) return 'collection';
	}

	return typeof item;
};

typeOf checks for specific properties on the object in question to determine its descriptive type. Simple, right? Note the $family() check within typeOf; each Type (Array, Function, Date, etc.) instance is given a $family method which returns its type. Let's try a few typeOf calls:

typeof document.body;  // returns "object"
typeOf(document.body);  // returns "element"

typeof new Date();  // returns "object"
typeOf(new Date());  // returns "date"

typeof [];  // returns "object"
typeOf([]);  // returns "array"

typeOf is an awesome utility function, right? Getting a more detailed object type than simply "object" can be hugely help in validating the object before using it. typeOf is just another awesome utility within the MooTools JavaScript framework.

Recent Features

  • By
    Camera and Video Control with HTML5

    Client-side APIs on mobile and desktop devices are quickly providing the same APIs.  Of course our mobile devices got access to some of these APIs first, but those APIs are slowly making their way to the desktop.  One of those APIs is the getUserMedia API...

  • By
    Chris Coyier’s Favorite CodePen Demos

    David asked me if I'd be up for a guest post picking out some of my favorite Pens from CodePen. A daunting task! There are so many! I managed to pick a few though that have blown me away over the past few months. If you...

Incredible Demos

  • By
    AJAX Page Loads Using MooTools Fx.Explode

    Note: All credit for Fx.Explode goes to Jan Kassens. One of the awesome pieces of code in MooTools Core Developer Jan Kassens' sandbox is his Fx.Explode functionality. When you click on any of the designated Fx.Explode elements, the elements "explode" off of the...

  • By
    JavaScript Copy to Clipboard

    "Copy to clipboard" functionality is something we all use dozens of times daily but the client side API around it has always been lacking; some older APIs and browser implementations required a scary "are you sure?"-style dialog before the content would be copied to clipboard -- not great for...

Discussion

  1. I use the regular “typeOf” to determine if classes are present, but the MooTools typeOf is much better, and great for making sure variables are the correct type. I wish more plugin coders would return robust error messages with these kinds of checks.

  2. Nice one !!!!!!

  3. Lorenzo

    Anyone knows if Mootools’ typeOf is more reliable than standard typeof when I want to check if something is a function or not?

    var a = (function() { return true; });
    var b = { name: 'value' };
    // typeof(a) == typeOf(a) == 'function' is always TRUE?
    // typeof(b) == typeOf(b) != 'function' is always TRUE?
    
  4. Mootools supports another type check – the Type Object.
    Type.isNumber(var), Type.isObject() etc.

    This is nowhere in the docs (except once used in an example on the Array page). It is shorter and more semantic when you are checking for one type, don’t know why it is hidden.

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