JavaScript Merge Sort

mergeSort.js

//Merge Sort

Array.prototype.mergeSort = function() {

  var thiz = this;
  if (this.length <= 1) {
    return this;
  }
  //split left and right 
  var left = [], right = [];
  var mid = Math.floor(thiz.length/2);
  right = thiz.slice(mid);
  left = thiz.slice(0, mid);
  return merge(left.mergeSort(), right.mergeSort());

  
  function merge(a, b) {
    var m = [];
    while (a.length && b.length) {
      if (a[0] < b[0]) {
        m.push(a.shift());
      } else {
        m.push(b.shift());
      }
    }
    if (a.length > 0) {
      m = m.concat(a);
    }
    if (b.length > 0) {
      m = m.concat(b);
    }
    return m;
  }
};


var a = [123,12,3,1534,75,1,99];
console.log(a.mergeSort());