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
    Write Simple, Elegant and Maintainable Media Queries with Sass

    I spent a few months experimenting with different approaches for writing simple, elegant and maintainable media queries with Sass. Each solution had something that I really liked, but I couldn't find one that covered everything I needed to do, so I ventured into creating my...

  • By
    CSS Filters

    CSS filter support recently landed within WebKit nightlies. CSS filters provide a method for modifying the rendering of a basic DOM element, image, or video. CSS filters allow for blurring, warping, and modifying the color intensity of elements. Let's have...

Incredible Demos

  • By
    CSS Text Overlap

    One of the important functions of CSS is to position elements. Margin, padding, top, left, right, bottom, position, and z-index are just a few of the major players in CSS positioning. By using the above spacing...

  • By
    dwImageProtector Plugin for jQuery

    I've always been curious about the jQuery JavaScript library. jQuery has captured the hearts of web designers and developers everywhere and I've always wondered why. I've been told it's easy, which is probably why designers were so quick to adopt it NOT that designers...

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!