How to determine if a number is odd in JavaScript

Question

Can anyone point me to some code to determine if a number in JavaScript is even or odd?

Answer 1

I'd implement this to return a boolean:

function isOdd (n) {
    return !!(n % 2);
    // or ((n % 2) !== 0).
}

It'll work on both unsigned and signed numbers. When the modulus return -1 or 1 it'll get translated to true.

Non-modulus solution:

var is_finite = isFinite;
var is_nan = isNaN;

function isOdd (discriminant) {
    if (is_nan(discriminant) && !is_finite(discriminant)) {
        return false;
    }

    // Unsigned numbers
    if (discriminant >= 0) {
        while (discriminant >= 1) discriminant -= 2;

    // Signed numbers
    } else {
        if (discriminant === -1) return true;
        while (discriminant <= -1) discriminant += 2;
    }

    return !!discriminant;
}