http://www.cnblogs.com/yjmyzz/archive/2009/10/20/1586896.html
var arrDemo = new Array();
arrDemo[0] = 10;
arrDemo[1] = 50;
arrDemo[2] = 51;
arrDemo[3] = 100;
arrDemo.sort(); //调用sort方法后,数组本身会被改变,即影响原数组
alert(arrDemo);//10,100,50,51 默认情况下sort方法是按ascii字母顺序排序的,而非我们认为是按数字大小排序
arrDemo.sort(function(a,b){return a>b?1:-1});//从小到大排序
alert(arrDemo);//10,50,51,100
arrDemo.sort(function(a,b){return a<b?1:-1});//从大到小排序
alert(arrDemo);//100,51,50,10