Implementing an Array.count() Method in JavaScript
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?
Discussion
Be Heard!
Share your thoughts with fellow developers of all skill levels! I want to hear from you!
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. :)
Do you do this for strings as well?
@Binny: No, I don’t. Just arrays.
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.
Correction to my previous post:
the second code snippet would be:
var myOtherArray = [];
myOtherArray[100] = ‘one’;
and its length property would actually return 101.
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;
}