08-merge-sort.js

function merge(left, right) {
  var result = [];

  while (left.length && right.length) {
    if (left[0] <= right[0]) {
      result.push(left.shift());
    } else {
      result.push(right.shift());
    }
  }

  while (left.length) {
    result.push(left.shift());
  }

  while (right.length) {
    result.push(right.shift());
  }

  return result;
}

function mergeSort(array) {
  var len = array.length;
  if (len < 2) {
    return array;
  }

  var middle = Math.floor(len / 2),
    left = array.slice(0, middle),
    right = array.slice(middle);
  return merge(mergeSort(left), mergeSort(right));
}

(function(sort) {
  var random = function(max) {
    var array = [];
    for (var i = 0; i < max; i++) {
      array[i] = i;
    }
    array.sort(function() {
      return 0.5 - Math.random();
    });
    return array;
  };

  var test = function(count) {
    for (var i = 0; i < count; i++) {
      var array = random(10);
      console.log('[No.' + (i + 1) + '] begin: ', array);
      console.time('time');
      console.log('[No.' + (i + 1) + '] end: ', sort(array));
      console.timeEnd('time');
    }
  };

  test(3);
}(mergeSort));