JavaScript Remainder Operator

Summary: in this tutorial, you’ll learn about the JavaScript remainder operator (%) to get the remainder of a number divided by another number.

Introduction to the JavaScript remainder operator

JavaScript uses the % to represent the remainder operator. The remainder operator returns the remainder left over when one value is divided by another value.

Here’s the syntax of the remainder operator:

dividend % divisor

The following shows the equation for the remainder:

dividend = divisor * quotient + remainder
where |remainder| < |divisor|

In this equation, the dividend, divisor, quotient, and remainder are all integers. The sign of the remainder is the same as the sign of the dividend.

The sign of the remainder is the same as the sign of the dividend.

JavaScript remainder operator examples

Let’s take some examples of using the JavaScript remainder operator.

1) Using the remainder operator with a positive dividend example

The following example shows how to use the remainder operator with a positive dividend:

let remainder = 5 % -2;
console.log(remainder); // 1

remainder = 5 % 2;
console.log(remainder); // 1Code language: JavaScript (javascript)

2) Using the remainder operator with a negative dividend example

The following example uses the remainder operator with a negative dividend:

let remainder = -5 % 3;
console.log(remainder); // -2

remainder = -5 % -3;
console.log(remainder); // -2Code language: JavaScript (javascript)

3) Using the remainder operator special values

If a dividend is an Infinity and a divisor is a finite number, the remainder is NaN. For example:

let remainder = Infinity % 2;
console.log(remainder); // NaNCode language: JavaScript (javascript)

If a dividend is a finite number and a divisor is zero, the remainder is NaN:

let remainder = 10 % 0;
console.log(remainder); // NaNCode language: JavaScript (javascript)

If both dividend and divisor are Infinity, the remainder is NaN:

let remainder = Infinity % Infinity;
console.log(remainder); // NaNCode language: JavaScript (javascript)

If a dividend is a finite number and the divisor is an Infinity, the remainder is the dividend. For example:

let remainder = 10 % Infinity;
console.log(remainder); // 10Code language: JavaScript (javascript)

If the dividend is zero and the divisor is non-zero, the remainder is zero:

let remainder = 0 % 10;
console.log(remainder); // 0Code language: JavaScript (javascript)

If either dividend or divisor is not a number, it’s converted to a number using the Number() function and applied the above rules. For example:

let remainder = '10' % 3;
console.log(remainder); // 1Code language: JavaScript (javascript)

Using the remainder operator to check if a number is an odd number

To check if a number is an odd number, you use the remainder operator (%) like the following example:

let num = 13;
let isOdd = num % 2;Code language: JavaScript (javascript)

In this example, if the num is an odd number, the remainder is one. But if the num is an even number, the remainder is zero.

Later, you’ll learn how to define a function that returns true if a number is odd or false otherwise like this:

function isOdd(num) {
  return num % 2;
}Code language: JavaScript (javascript)

Or using an arrow function in ES6:

const isOdd = (num) => num % 2;Code language: JavaScript (javascript)

Remainder vs Modulo operator

In JavaScript, the remainder operator (%) is not the modulo operator.

If you have been working with Python, you may find the % represents the modulo operator in this language. However, this is not the case in JavaScript.

To get a modulo in JavaScript, you use the following expression:

((dividend % divisor) + divisor) % divisor

Or wrap it in a function:

const mod = (dividend, divisor) => ((dividend % divisor) + divisor) % divisor;Code language: JavaScript (javascript)

If the division and divisor have the same sign, the remainder and modulo operators return the same result. Otherwise, they return different results.

For example:

const mod = (dividend, divisor) => ((dividend % divisor) + divisor) % divisor;

// dividen and divisor have the same sign
console.log('remainder:', 5 % 3); // 2
console.log('modulo:', mod(5, 3)); // 2

// dividen and divisor have the different signs
console.log('remainder:', -5 % 3); // -2
console.log('modulo:', mod(-5, 3)); // 1
Code language: JavaScript (javascript)

Output:

remainder: 2
modulo: 2
remainder: -2
modulo: 1Code language: HTTP (http)

Summary

• Use the JavaScript remainder operator (%) get the remainder of a value divided by another value.