JavaScript % (modulo) gives a negative result for negative numbers

javascript math modulo

Number.prototype.mod = function(n) {    return ((this%n)+n)%n;};

javascript math modulo

Using Number.prototype is SLOW, because each time you use the prototype method your number is wrapped in an Object. Instead of this:

Number.prototype.mod = function(n) {  return ((this % n) + n) % n;}

Use:

function mod(n, m) {  return ((n % m) + m) % m;}

~97% faster than using prototype. If performance is of importance to you of course..

javascript math modulo

The % operator in JavaScript is the remainder operator, not the modulo operator (the main difference being in how negative numbers are treated):

-1 % 8 // -1, not 7

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