How can I use modulo operator (%) ... for JavaScript projects? ... Someone might want to rename this question from modulo to remainder because it pops up in Google searches for a modulo operator in JS. ... It's the remainder operator and is used to get the remainder after integer division... More on stackoverflow.com

A quick peek at the documentation would reveal that % in JavaScript is not modulo, it's the remainder operator (or can be found in the ECMAScript specification ). This is confusing to many people, and unfortunately articles like these don't help by using the wrong terminology. The difference occurs when one of the values is negative. -21 % 4 The result of this is 3 for "mod" and -1 for "rem". This can be confusing behavior, if for example, to implement an isOdd function, you might think of something like this: function isOdd(n) { return n % 2 === 1 } However, this is wrong! It returns false for an input of -1. More on reddit.com

1. If you're going to compute the remainder rem anyway, you can get the quotient div faster without flooring: (y - rem) / x. 2. By the way the modulo operation by Donald Knuth's recommended definition (sign-matches-divisor, not the remainder i.e. Euclidean modulus, nor the JavaScript ... More on stackoverflow.com

Of course it will not be standardized, because changing how the mod works would break millions of existing programs. The "why" is difficult. Maybe some used the definition that would make the implementation faster with the available processors, or the one more coherent from a nathematical point of view. In practice, most of times you use positive operands. I've programmed as an amateur for decads before encountering a negative operand (last week), so knowing it was tricky, I checked it. More on reddit.com