数组排序

升序

function sortNum(a,b){
return a-b;
}
var arr=[2,5,6,7,1,0,-1];
arr.sort(sortNum);
//[-1, 0, 1, 2, 5, 6, 7]

降序

function sortNum(a,b){
return b-a;
}
var arr=[2,5,6,7,1,0,-1];
arr.sort(sortNum);
//[7, 6, 5, 2, 1, 0, -1]