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

Many people misunderstand the meaning of odd

• isOdd("str") should be false.
  Only an integer can be odd.
• isOdd(1.223) and isOdd(-1.223) should be false.
  A float is not an integer.
• isOdd(0) should be false.
  Zero is an even integer (https://en.wikipedia.org/wiki/Parity_of_zero).
• isOdd(-1) should be true.
  It's an odd integer.

Solution

function isOdd(n) {

  // Must be a number
  if (isNaN(n)) {
    return false;
  }

  // Number must not be a float
  if ((n % 1) !== 0) {
    return false;
  }

  // Integer must not be equal to zero
  if (n === 0) {
    return false;
  }

  // Integer must be odd
  if ((n % 2) !== 0) {
    return true;
  }

  return false;
}

JS Fiddle (if needed): https://jsfiddle.net/9dzdv593/8/

1-liner

Javascript 1-liner solution. For those who don't care about readability.

const isOdd = n => !(isNaN(n) && ((n % 1) !== 0) && (n === 0)) && ((n % 2) !== 0) ? true : false;