Given a number and an array of numbers, return the number in an array that is closest to that number.

closest.js

/*
closest(0.5, [0, 1, 2, 3]); // 1
closest(0.4, [0, 1, 2, 3]); // 0
*/

function closest (num, arr) {
  if (!arr || !arr.length) {
    return;
  }
  return arr.slice(0).sort(function (a, b) {
    var diffA = Math.abs(a - num),
      diffB = Math.abs(b - num);
    if (diffA < diffB) {
      return -1;
    } else if (diffA === diffB) {
      return a > b ? -1 : 1;
    }
    return 1;
  })[0];
}