Treehouse

Implementing an Array.count() Method in JavaScript

By on  

As much as I write about MooTools on my blog, I spend most of my work day knee-deep in PHP. As you probably know, one way to get the size of an array in PHP is to use the count() function:

echo count($my_array);

In JavaScript, the way to get the size of an array is to use the length property, like this:

alert(my_array.length);

For some reason, I absolutely hate the ".length" way of retrieving the length of an array. For this reason, I've implement the count() method into JavaScript:

Array.prototype.count = function() {
	return this.length;
};

The count() habit is difficult to break, so why try?

ydkjs-5.png

Recent Features

  • Create a CSS Cube

    CSS cubes really showcase what CSS has become over the years, evolving from simple color and dimension directives to a language capable of creating deep, creative visuals.  Add animation and you've got something really neat.  Unfortunately each CSS cube tutorial I've read is a bit...

  • Detect DOM Node Insertions with JavaScript and CSS Animations

    I work with an awesome cast of developers at Mozilla, and one of them in Daniel Buchner. Daniel's shared with me an awesome strategy for detecting when nodes have been injected into a parent node without using the deprecated DOM Events API....

Incredible Demos

  • CSS Animations Between Media Queries

    CSS animations are right up there with sliced bread. CSS animations are efficient because they can be hardware accelerated, they require no JavaScript overhead, and they are composed of very little CSS code. Quite often we add CSS transforms to elements via CSS during...

  • Send Email Notifications for Broken Images Using MooTools AJAX

    One of the little known JavaScript events is the image onError event. This event is triggered when an image 404's out because it doesn't exist. Broken images can make your website look unprofessional and it's important to fix broken images as soon as possible....

Discussion

  1. Thanks for your blog. you offer great advice and tutorials and for some odd reason, if I am looking to see how to complete a task, you have a tutorial on it or at least an idea on the concept I am trying to achieve; so thanks David. Although this post came about 2 days too late. :)

  2. Do you do this for strings as well?

  3. @Binny: No, I don’t. Just arrays.

  4. Jason

    This is all fine and well, but length is fundamentally different from count.

    Take the following example:

    var myArray = ['one', 'two', 'three'];
    // myArray.length == 3, as we would expect

    var myOtherArray[100] = ‘one';
    //myArray.length == 100, NOT 1

    Even though we only have 1 item in the array, ‘length’ refers to the largest index + 1. Unlike PHP where we can use numeric keys and strings for indexes in an ad hoc way and still get an accurate count via count(), in JS it’s not quite the same.

    In a way, this is just splitting hairs, but a lot of people already don’t understand JS’s length property, and referring to it as “count” only serves to further the confusion.

  5. Jason

    Correction to my previous post:

    the second code snippet would be:

    var myOtherArray = [];
    myOtherArray[100] = ‘one';

    and its length property would actually return 101.

  6. riv

    That’s right and that’s what I was expecting when searching for count on js. This should do it:

    function count(array)
    {
        var c = 0;
        for(i in array) // in returns key, not object
            if(array[i] != undefined)
                c++;
    
    return c;
    }
    
    • Riv, thats a much better form of the count use. Its surprising that this is not built into javascript.

  7. Christian
    Array.prototype.count = function () {
        for (k in this) { if (this[k].constructor !== Function) { this.length++; } };
        return this.length;
    }
    
  8. I think it’s okay for personal project but it has a counter side when you are in enterprise. The maintainability is harder when people use custom extension (prototype existing framework object). It cane be confusing. In some case, I have seen people creating function to simply get an object inside an array. I think this should be used with parsimony. But, it’s just my opinion…

  9. Iskren Antonov
    Array.prototype.count = function () {
    	var counter = 0; // Initializing main counter
    	for(i in this) // Looping through elements
    		if(typeof this[i] != "undefined") // If empty it's undefined
    			counter++; // Counting not empty elements
    	return counter-1; // Excepting own function
    }
    

    This is a working one. It counts function elements too.

  10. Lineo

    I’ve just bumped into learning Js, I try to be as attentive as possible but, I don’t find a way. So, may any one help me how to understand Js programming.

  11. Rowan Adinghey
    Array.prototype.count = function (a) {
    	var c = 0;
    	for(var i = 0; i < this.length; i++) {
    		if(typeof(this[i]) !== "undefined") {
    			if(typeof(this[i]) == "string" && this[i].length == 0) {
    			} else { 
    				c++;
    			}
    		}
    	}
    	return c;
    }
    

    OR

    
    count = function (a) {
    	var c = 0;
    	for(var i = 0; i < this.length; i++) {
    		if(typeof(a[i]) !== "undefined") {
    			if(typeof(a[i]) == "string" && a[i].length == 0) {
    			} else { 
    				c++;
    			}
    		}
    	}
    	return c;
    }
    

    Wow, no functionality to edit comments? What is this, the year 2001?

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