Implementing an Array.count() Method in JavaScript

Discussion

1. Rich

   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. Binny V A

   Do you do this for strings as well?
3. david

   @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;
   }
   
• Everwebby

  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. Patrick

   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?
12. Dmitri Pavlutin

    Querying the length is faster than invoking a method, but the habit of using .count() is interesting.
    In python is used len([1, 2, 3]) function to get the count, so the JavaScript’s length is not so bad :).