js中Array.sort()实现原理

定义：sort() 方法用于对数组的元素进行排序。
api语法：arrayObject.sort(sortby)；参数sortby可选，用于规定排序规则，必须是函数。
具体是如何实现的？
V8 引擎 sort 函数只给出了两种排序分别是： InsertionSort 和 QuickSort，数组长度小于等于 10 的用插入排序 InsertionSort，比10大的数组则使用快速排序 QuickSort
地址：https://github.com/v8/v8/blob/master/src/js/array.js
Mozilla/Firefox : 归并排序（jsarray.c 源码）
Webkit ：底层实现用了 C++ 库中的 qsort() 方法（JSArray.cpp 源码）

function InnerArraySort(array, length, comparefn) {  // In-place QuickSort algorithm.  // For short (length <= 10) arrays, insertion sort is used for efficiency.  if (!IS_CALLABLE(comparefn)) {    comparefn = function (x, y) {      if (x === y) return 0;      if (%_IsSmi(x) && %_IsSmi(y)) {        return %SmiLexicographicCompare(x, y);      }      x = TO_STRING(x);      y = TO_STRING(y);      if (x == y) return 0;      else return x < y ? -1 : 1;    };  }  function InsertionSort(a, from, to) {    for (var i = from + 1; i < to; i++) {      var element = a[i];      for (var j = i - 1; j >= from; j--) {        var tmp = a[j];        var order = comparefn(tmp, element);        if (order > 0) {          a[j + 1] = tmp;        } else {          break;        }      }      a[j + 1] = element;    }  };  function GetThirdIndex(a, from, to) {    var t_array = new InternalArray();    // Use both 'from' and 'to' to determine the pivot candidates.    var increment = 200 + ((to - from) & 15);    var j = 0;    from += 1;    to -= 1;    for (var i = from; i < to; i += increment) {      t_array[j] = [i, a[i]];      j++;    }    t_array.sort(function(a, b) {      return comparefn(a[1], b[1]);    });    var third_index = t_array[t_array.length >> 1][0];    return third_index;  }  function QuickSort(a, from, to) {    var third_index = 0;    while (true) {      // Insertion sort is faster for short arrays.      if (to - from <= 10) {        InsertionSort(a, from, to);        return;      }      if (to - from > 1000) {        third_index = GetThirdIndex(a, from, to);      } else {        third_index = from + ((to - from) >> 1);      }      // Find a pivot as the median of first, last and middle element.      var v0 = a[from];      var v1 = a[to - 1];      var v2 = a[third_index];      var c01 = comparefn(v0, v1);      if (c01 > 0) {        // v1 < v0, so swap them.        var tmp = v0;        v0 = v1;        v1 = tmp;      } // v0 <= v1.      var c02 = comparefn(v0, v2);      if (c02 >= 0) {        // v2 <= v0 <= v1.        var tmp = v0;        v0 = v2;        v2 = v1;        v1 = tmp;      } else {        // v0 <= v1 && v0 < v2        var c12 = comparefn(v1, v2);        if (c12 > 0) {          // v0 <= v2 < v1          var tmp = v1;          v1 = v2;          v2 = tmp;        }      }      // v0 <= v1 <= v2      a[from] = v0;      a[to - 1] = v2;      var pivot = v1;      var low_end = from + 1;   // Upper bound of elements lower than pivot.      var high_start = to - 1;  // Lower bound of elements greater than pivot.      a[third_index] = a[low_end];      a[low_end] = pivot;      // From low_end to i are elements equal to pivot.      // From i to high_start are elements that haven't been compared yet.      partition: for (var i = low_end + 1; i < high_start; i++) {        var element = a[i];        var order = comparefn(element, pivot);        if (order < 0) {          a[i] = a[low_end];          a[low_end] = element;          low_end++;        } else if (order > 0) {          do {            high_start--;            if (high_start == i) break partition;            var top_elem = a[high_start];            order = comparefn(top_elem, pivot);          } while (order > 0);          a[i] = a[high_start];          a[high_start] = element;          if (order < 0) {            element = a[i];            a[i] = a[low_end];            a[low_end] = element;            low_end++;          }        }      }      if (to - high_start < low_end - from) {        QuickSort(a, high_start, to);        to = low_end;      } else {        QuickSort(a, from, low_end);        from = high_start;      }    }  };

arrayObject.sort(sortby) 的使用方法
实例1：

var arr = new Array(6)   arr[0] = "George"   arr[1] = "John"   arr[2] = "Tom"   arr[3] = "Jane"   arr[4] = "Adrew"   arr[5] = "mary"   console.log(arr + "<br />")   console.log(arr.sort()+ "<br />")  console.log(arr + "<br />")  

输出：

George,John,Tom,Jane,Adrew,maryAdrew,George,Jane,John,Tom,maryAdrew,George,Jane,John,Tom,mary

实例2：
当需要对数字进行大小排序时必须使用排序函数

function sortNumber(a,b){return a - b}var arr = new Array(6)arr[0] = "10"arr[1] = "5"arr[2] = "40"arr[3] = "25"arr[4] = "1000"arr[5] = "1"document.write(arr + "<br />")document.write(arr.sort(sortNumber))

输出：

10,5,40,25,1000,11,5,10,25,40,1000

从大到小:

function sortNumber(a,b){return b - a}

输出：

    10,5,40,25,1000,1    1000,40,25,10,5,1