gistfile1.txt

   var test = 24,
arr = [76,56,22,89,74].sort(); // just sort it generally if not sure about input, not really time consuming

function getClosest(test, arr) {
  var num = 0, result = 0;
  var flag = 0;
  for(var i = 0; i < arr.length; i++) {
    num = arr[i];
    if(num < test) {
      result = num;
      flag = 1;
    }else if (num == test) {
      result = num;
      break;
    }else if (flag == 1) {
      if ((num - test) < (Math.abs(arr[i-1] - test))){
        result = num;
      }
      break;
    }else{
      break;
    }
  }
  return result;
}
console.log(getClosest(test, arr));