归并排序实现原理：把一系列排好序的子序列合并成一个大的完整有序序列。在递归算法中归并排序算是一个比较典型的例子了，下面是使用javascript实现的归并排序算法：
<!DOCTYPE html>
<html>
<head>
<title></title>
</head>
<body>
<script>
var merge = function (unsorted, first, mid, last, sorted){
var i = first, j = mid;
var k = 0;
while (i < mid && j < last){
if (unsorted[i] < unsorted[j])
sorted[k++] = unsorted[i++];
else
sorted[k++] = unsorted[j++];
}
while (i < mid){
sorted[k++] = unsorted[i++];
}
while (j < last){
sorted[k++] = unsorted[j++];
}
for (var v = 0; v < k; v++) {
unsorted[first + v] = sorted[v]; // 复制到原数组中
}
};
var merge_sort = function (unsorted, first, last, sorted){
if (first + 1 < last)
{
var mid = Math.floor((first + last) / 2);
merge_sort(unsorted, first, mid, sorted);
merge_sort(unsorted, mid, last, sorted);
merge(unsorted, first, mid, last, sorted);
}
};
// var nums = [6,10,1,9,4,8,2,7,3,5];
var nums = [6,2,8,3];
var sorted = [];
console.log("merge before
");
console.log(nums.toString());
console.log("merge after
");
merge_sort(nums, 0, nums.length, sorted);
console.log(nums.toString());
</script>
</body>
</html>
参考：http://www.cnblogs.com/jillzhang/archive/2007/09/16/894936.html