JavaScript Remainder (%) Operator

The JavaScript remainder operator % returns the remainder left after dividing one number by another. It is commonly used for even/odd checks, repeating patterns, cycling counters, and grouping values.

console.log(123 % 5); // 3
console.log(12 % 2);  // 0

Show Table of Contents ↓

Remainder operator syntax Top ↑

dividend % divisor

Although this operator is often called “modulus” in everyday programming, JavaScript's % follows remainder semantics: the sign of a non-zero result follows the dividend.

Check whether a number is even or odd Top ↑

const value = 27;
if (value % 2 === 0) {
  console.log("Even");
} else {
  console.log("Odd");
}

Negative numbers: remainder is not always mathematical modulo Top ↑

console.log(-13 % 5); // -3
console.log(13 % -5); // 3

If you need a non-negative wrap-around result for a positive modulus n, normalize it:

function mod(value, n) {
  return ((value % n) + n) % n;
}
console.log(mod(-1, 5)); // 4

Reset a repeating counter Top ↑

let counter = 0;
const cycleLength = 30;

counter = (counter + 1) % cycleLength;
console.log(counter);

See the timer tutorial and resetting-counter demo.

Change every alternate array item Top ↑

const scripts = ["PHP", "ASP", "JavaScript", "HTML"];

scripts.forEach((name, index) => {
  const group = index % 2 === 0 ? "even index" : "odd index";
  console.log(name, group);
});

See displaying array elements, the HTML span tutorial, and the alternate-row demo.

Wrap an array index Top ↑

const items = ["A", "B", "C"];
let index = 2;
index = (index + 1) % items.length;
console.log(items[index]); // A

Remainder with a zero divisor Top ↑

console.log(10 % 0); // NaN

Remainder with decimal values Top ↑

The % operator also works with finite decimal Number values. Because JavaScript uses binary floating-point numbers, decimal remainders can show representation effects.

console.log(5.5 % 2); // 1.5
console.log(0.3 % 0.1); // may expose floating-point precision effects

Remainder with BigInt Top ↑

The operator also works with BigInt when both operands are BigInts. Do not mix a Number and a BigInt in the same arithmetic operation.

console.log(17n % 5n); // 2n

Common remainder mistakes Top ↑

The main mistake is assuming % always returns a non-negative mathematical modulo. With a negative dividend, JavaScript can return a negative remainder. Normalize it when you need cyclic indexes that must stay in the range 0 through n - 1.

Remainder operator demos Top ↑

Try the alternate-item demo and counter-reset demo.

Math.abs() →

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

About the author   Watch on YouTube

Connect: