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
    CSS Gradients

    With CSS border-radius, I showed you how CSS can bridge the gap between design and development by adding rounded corners to elements.  CSS gradients are another step in that direction.  Now that CSS gradients are supported in Internet Explorer 8+, Firefox, Safari, and Chrome...

  • By
    Facebook Open Graph META Tags

    It's no secret that Facebook has become a major traffic driver for all types of websites.  Nowadays even large corporations steer consumers toward their Facebook pages instead of the corporate websites directly.  And of course there are Facebook "Like" and "Recommend" widgets on every website.  One...

Incredible Demos

  • By
    pointer Media Query

    As more devices emerge and differences in device interaction are implemented, the more important good CSS code will become.  In order to write good CSS, we need some indicator about device capabilities.  We've used CSS media queries thus far, with checks for max-width and pixel ratios.

  • By
    MooTools Clipboard Plugin

    The ability to place content into a user's clipboard can be extremely convenient for the user. Instead of clicking and dragging down what could be a lengthy document, the user can copy the contents of a specific area by a single click of a mouse.

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!