Looping in JavaScript to count non-null and non-empty values

In JavaScript, counting non-null and non-empty values in an array is a common task. This article demonstrates how to use forEach() to iterate through an array and count valid values.

Basic Array Example

Let's start with an array containing subject names:

let subjectNames = ['JavaScript', 'Angular', 'AngularJS', 'Java'];
console.log("Original array:", subjectNames);

Original array: [ 'JavaScript', 'Angular', 'AngularJS', 'Java' ]

Using forEach() to Count Valid Values

The forEach() method executes a function for each array element. Here's the syntax:

yourArrayName.forEach(element => {
    // Your logic here
});

Counting Non-Null and Non-Empty Values

To count valid values, we use a counter variable and check each element:

let subjectNames = ['JavaScript', 'Angular', 'AngularJS', 'Java'];
var count = 0;

subjectNames.forEach(subject => {
    if(subject != '' && subject != null) {
        count += 1;
    }
});

console.log("Number of valid subjects: " + count);

Number of valid subjects: 4

Handling Mixed Data Types

Here's a more comprehensive example with null, empty, and undefined values:

let mixedData = ['JavaScript', '', null, 'Angular', undefined, 'Java', ' '];
var validCount = 0;

mixedData.forEach(item => {
    if(item != null && item != undefined && item.trim() !== '') {
        validCount += 1;
    }
});

console.log("Mixed array:", mixedData);
console.log("Valid items count:", validCount);

Mixed array: [ 'JavaScript', '', null, 'Angular', undefined, 'Java', ' ' ]
Valid items count: 3

Alternative Methods

You can also use the filter() method for a more concise approach:

let subjects = ['JavaScript', '', null, 'Angular', undefined, 'Java'];

// Using filter method
let validItems = subjects.filter(item => item != null && item != undefined && item !== '');
console.log("Valid count using filter:", validItems.length);

// Using reduce method
let countUsingReduce = subjects.reduce((count, item) => {
    return (item != null && item != undefined && item !== '') ? count + 1 : count;
}, 0);
console.log("Valid count using reduce:", countUsingReduce);

Valid count using filter: 3
Valid count using reduce: 3

Comparison of Methods

Conclusion

Use forEach() with conditional checks to count non-null and non-empty values. For simpler cases, consider filter().length for better readability.