Using the Array.prototype.filter Method

The Array.prototype.filter method enables us to create a new array that contains only the elements that satisfy a particular condition. By utilizing the length property of the filtered array, we can easily count the qualifying items.

For example, consider the following code:

const arr = [1, 2, 3, 5, 2, 8, 9, 2];

const numEvens = arr.filter(x => x % 2 === 0).length;

console.log(numEvens);

In this snippet, we have an array named arr filled with numbers. To count the even numbers, we apply the filter method with a callback that checks if a number is even (x % 2 === 0). The result is an array of even numbers, and by accessing its length, we find that numEvens equals 4, as shown in the console log.

The first video titled "JavaScript Problem: Counting the Number of Occurrences in an Array" provides further insights into counting elements in arrays.

Using the Array.prototype.reduce Method

Another approach to counting specific elements is through the Array.prototype.reduce method. Here's how you can count the even numbers using reduce:

const arr = [1, 2, 3, 5, 2, 8, 9, 2];

const numEvens = arr.reduce((total, x) => (x % 2 === 0 ? total + 1 : total), 0);

console.log(numEvens);

In this example, we invoke reduce with a callback that accepts two parameters: total and x. The total variable holds the cumulative count so far, while x represents the current element. If x is even (x % 2 === 0), we increment the total by 1; otherwise, we return the current total. The second argument, 0, initializes the total. Consequently, the value of numEvens remains consistent with our previous method.

The second video titled "Array: Get Element Count" elaborates on how to retrieve element counts effectively.