Modulo use cases because math is hard

modulo-use-cases.js

// find if number is even or odd
const isEven = val => val % 2 === 0;
isEven(11); //false
isEven(22); //true

// do time related things...
const formatMovieTime = val => {
  const hours = Math.floor(val / 60); //get the hours, discard any remainder via `floor`
  const mins = val % 60; //get the remainder of minutes left over as an integer
  return `${hours}:${mins < 10 ? '0' + mins : mins}`;
};
//let's say these are movie run times, which are always in just minutes for some reason
formatMovieTime(121); // 2:01
formatMovieTime(165); // 2:45
formatMovieTime(180); // 3:00

// convert military time to normal, human readable time
const militaryTimeToNormalTime = str => {
  const split = str.split(':');
  return `${split.shift() % 12}:${split.pop()}`
};
militaryTimeToNormalTime('13:59') // 1:59
militaryTimeToNormalTime('2:01') // 2:01

more ideas: https://betterexplained.com/articles/fun-with-modular-arithmetic/