var a = ['1'];
a[5] = 52;
a.length //这儿的结果是6，也就是说，中间的key会自动补全，而值呢，是undefined

test = {}; //空json对像
test['firstname'] = "tank"; //添加二个元素
test['lastname'] = "zhang";
console.log(test); //查看
delete test['lastname']; //删除json中的某个元素
console.log(test);

test1 = [{"name":"tank","total":"100"},{"name":"zhang","total":"23"},{"name":"hao","total":"325"}];
add = {"name":"may"};
test1.push(add); //添加一个元素
console.log(test1);
delete test1[2]; //删除一个元素
console.log(test1);

test = ["100","23","325"]; //定义个数组
function sortNumber(a,b) //定义排序方法
{
   return a - b
}
test1_sort=test.sort(sortNumber);
console.log(test1_sort);

test1 = [{"name":"tank","total":"100"},{"name":"zhang","total":"23"},{"name":"hao","total":"325"}];
sort_by = function(field, reverse, primer){ //定义排序方法
  var key = primer ?
    function(x) {return primer(x[field])} :
    function(x) {return x[field]};
  reverse = [-1, 1][+!!reverse];
  return function (a, b) {
    return a = key(a), b = key(b), reverse * ((a > b) - (b > a));
   }
}
test1_sort=test1.sort(sort_by('total', true, parseInt)); //根据total，升序排
console.log(test1_sort);
test1_sort=test1.sort(sort_by('name', false, '')); //根据name，倒序排
console.log(test1_sort);