Javascript array sort and unique

This is actually very simple. It is much easier to find unique values, if the values are sorted first:

function sort_unique(arr) {
  if (arr.length === 0) return arr;
  arr = arr.sort(function (a, b) { return a*1 - b*1; });
  var ret = [arr[0]];
  for (var i = 1; i < arr.length; i++) { //Start loop at 1: arr[0] can never be a duplicate
    if (arr[i-1] !== arr[i]) {
      ret.push(arr[i]);
    }
  }
  return ret;
}
console.log(sort_unique(['237','124','255','124','366','255']));
//["124", "237", "255", "366"]

You can now achieve the result in just one line of code.

Using new Set to reduce the array to unique set of values. Apply the sort method after to order the string values.

var myData=['237','124','255','124','366','255']

var uniqueAndSorted = [...new Set(myData)].sort() 

UPDATED for newer methods introduced in JavaScript since time of question.