JavaScript: How To Find The Number Of Times An Item Appears In An Array

Written 23 October 2021 •

If you have a Python background, you are probably familiar with the count method in the list class. The count method does not exist in JavaScript. For those unfamiliar with the count method, it counts the number of times an item appears in an array. For example, suppose we have a numbers array, and we want to find the number of times the number two appears in the array. In Python, we'd do it like this.

numbers = [1,2,3,4,5,2,3,4,2,4,2]
print(numbers.count(2)) # => 4

The code would return 4 because the number two appears four times in the array. Because this technique does not exist in JavaScript, I opted to write my own.

Code

Array.prototype.count = function (item) {
	return this.filter((x) => x === item).length;
};

Explanation

In the code above, I extended the Array class and added a new method called count through the prototype. The method takes an argument called item. It then filters the array and returns the length of the remaining items. Simple.

Using The Code

To utilise the code, simply construct an array and call the count method as shown below.

let names = ["David", "Walsh", "David", "Tania", "Lucretius"];
names.count("David"); //=> 2

Fellas, happy coding! 😄