数组对比，保留不存在的

//数组对比，获取不存在的
var obj = [];
for(var i =0,len = list.length;i<len;i++){
obj[list[i]] = 1;
}
for(var i =0,len = arr.length;i<len;i++){
obj[arr[i]] = obj[arr[i]]?2:1;
}
var i = 0;
for(var per in obj){
if(obj[per] == 1){
art[i++] = per;
}
}