140_modulo.js

/*
Write a function called "modulo".

Given 2 numbers, "modulo" returns the remainder after dividing num1 by num2.

It should behave as described in the canonical documentation (MDN) for the JavaScript remainder operator:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Remainder_()

Notes:
* Do NOT use the actual built-in modulo (aka "remainder") operator (%) in your implementation.
* 0 % ANYNUMBER = 0.
* ANYNUMBER % 0 = NaN.
* If either operand is NaN, then the result is NaN.
* Modulo always returns the sign of the first number.

var output = modulo(25, 4);
console.log(output); // --> 1
*/

function modulo(num1, num2) {
  if (num1 === 0) {
    return 0;
  } else if (typeof num1 !== 'number' || typeof num2 !== 'number' || num2 === 0) {
    return NaN;
  } else {
    var otherFactor = Math.floor(Math.abs(num1)/Math.abs(num2));
    var remainder = Math.abs(num1)-Math.abs(num2*otherFactor);
      if (num1 < 0) {return remainder * -1;}
      if (num1 > 0) {return remainder;}
  }
}