It's the remainder operator and is used to get the remainder after integer division. Lots of languages have it. For example:

10 % 3 // = 1 ; because 3 * 3 gets you 9, and 10 - 9 is 1.

Apparently it is not the same as the modulo operator entirely.

Answer from MarioDS on Stack Overflow
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W3Schools
w3schools.com โ€บ js โ€บ js_arithmetic.asp
JavaScript Arithmetic
The modulus operator (%) returns the division remainder. let x = 5; let y = 2; let z = x % y; Try it Yourself ยป ยท In arithmetic, the division of two integers produces a quotient and a remainder.
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Josh W. Comeau
joshwcomeau.com โ€บ javascript โ€บ modulo-operator
Understanding the JavaScript Modulo Operator โ€ข Josh W. Comeau
One of the most commonly-misunderstood operators is Modulo (%). In this tutorial, we'll unpack exactly what this little bugger does, and learn how it can help us solve practical problems.
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freeCodeCamp
freecodecamp.org โ€บ news โ€บ javascript-modulo-operator-how-to-use-the-modulus-in-js
JavaScript Modulo Operator โ€“ How to Use the Modulus in JS
November 7, 2024 - For example, 10 modulo 3 will be ... for JavaScript, you will use 10 % 3. It divides the first operand (the dividend) by the second operand (the divisor) and returns the remainder....
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MDN Web Docs
developer.mozilla.org โ€บ en-US โ€บ docs โ€บ Web โ€บ JavaScript โ€บ Reference โ€บ Operators โ€บ Remainder
Remainder (%) - JavaScript | MDN
For two values of the same sign, ... which can make them differ by one unit of d. To obtain a modulo in JavaScript, in place of n % d, use ((n % d) + d) % d....
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Mimo
mimo.org โ€บ glossary โ€บ javascript โ€บ modulo-operator
JavaScript Modulo Operator: Syntax, Usage, and Examples
Learn how JavaScript's modulo operator works with positive and negative numbers, floating points, and loops. Includes syntax, tips, and real examples.
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Mastering JS
masteringjs.io โ€บ tutorials โ€บ fundamentals โ€บ modulus
The Modulus Operator in JavaScript - Mastering JS
The modulus operator in JavaScript returns the remainder when the first operand is divided by the second operand. Here's what you need to know.
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AlgoCademy
algocademy.com โ€บ link
Modulo Operator in JavaScript | AlgoCademy
The modulo operator is a powerful tool in JavaScript that allows you to calculate remainders, check for even or odd numbers, cycle through array indices, and more. By mastering this operator, you can write more efficient and effective code.
Find elsewhere
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LogRocket
blog.logrocket.com โ€บ home โ€บ mastering the modulo operator in javascript: a complete guide
Mastering the modulo operator in JavaScript: A complete guide - LogRocket Blog
June 4, 2024 - For example, when we divide 10 by three, we get a quotient of three and a remainder of one. We can also write this as 1 (mod 3). In JavaScript, the modulo operator gets the remainder of a division operation.
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Codedamn
codedamn.com โ€บ news โ€บ javascript
JavaScript Modulo Operator Guide With Examples
June 3, 2023 - The modulo operator, represented by the percentage symbol (%), is a commonly used operator in JavaScript that returns the remainder of a division operation. In other words, it tells you what's left over after dividing two numbers.
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W3Schools
w3schools.com โ€บ js โ€บ tryit.asp
W3Schools online HTML editor
The W3Schools online code editor allows you to edit code and view the result in your browser
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GeeksforGeeks
geeksforgeeks.org โ€บ javascript โ€บ modulus-arithmetic-operator-in-javascript
Modulus(%) Arithmetic Operator in JavaScript - GeeksforGeeks
July 23, 2025 - The modulus (%) arithmetic operator in JavaScript returns the remainder after dividing one number by another.
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TutorialsPoint
tutorialspoint.com โ€บ What-is-Modulus-Operator-in-JavaScript
What is Modulus Operator (%) in JavaScript?
In the expression a % b, a is called dividend, while b is known as divisor. In case of the modulo, the expression ((a % b) + b) % b is used to find out the remainder, where the sign of the resultant remainder will be similar to the sign of the divisor, b in this case.
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Reddit
reddit.com โ€บ r/programming โ€บ understanding the javascript modulo operator
r/programming on Reddit: Understanding the JavaScript Modulo Operator
December 12, 2023 - The post explains the Modulo operator ... how we think about division, emphasizing that it's about dividing a number into equally-sized groups without fractional remainders....
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Delft Stack
delftstack.com โ€บ home โ€บ howto โ€บ javascript โ€บ javascript modulo
Modulo Operator(%) in JavaScript | Delft Stack
March 11, 2025 - Learn how to use the modulo operator (%) in JavaScript with this comprehensive tutorial. Explore its applications, check for even or odd numbers, and discover practical examples to enhance your coding skills. Ideal for beginners and experienced developers looking to master this essential operator.
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Codingem
codingem.com โ€บ home โ€บ javascript % operator: an ultimate guide to modulos
JavaScript % Operator: An Ultimate Guide to Modulos - codingem.com
July 10, 2025 - In JavaScript, you can use the % operator to calculate the remainder in division. The % operator is called the modulo operator.
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W3Schools
w3schools.com โ€บ js โ€บ tryit.asp
W3Schools Tryit Editor - JavaScript Arithmetic
The W3Schools online code editor allows you to edit code and view the result in your browser
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Career Karma
careerkarma.com โ€บ blog โ€บ javascript โ€บ javascript modulo: a how-to guide
JavaScript Modulo: A How-To Guide | Career Karma
December 1, 2023 - The modulo operator tells you what is left over when a number has been divided as many times as it can be. The remainder of 9 divided by 4 is 1. 4 goes into 9 twice. There is 1 left over.
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Jsremote
jsremote.jobs โ€บ tutorials โ€บ modulo
What is modulo in JavaScript? | Web developer jobs
When two numbers are divisible by the remainder, we have to define what operator will be responsible for it. Well, where there is a demand, there is a supply. In JavaScript we have a thing called modulo operator.