JS中数组去除重复

function outRepeat(a){
var hash=[],arr=[];
for (var i = 0; i < a.length; i++) {
hash[a[i]]!=null;
if(!hash[a[i]]){
arr.push(a[i]);
hash[a[i]]=true;
}
}
console.log(arr);
}
outRepeat([2,4,4,5,"a","a"]);//[2, 4, 5, "a"]

function outRepeat(a){
var hash=[],arr=[];
for (var i = 0,elem;(elem=a[i])!=null; i++) {
if(!hash[elem]){
arr.push(elem);
hash[elem]=true;
}
}
console.log(arr);
}
outRepeat([2,4,4,5,"a","a"]);//[2, 4, 5, "a"]

function outRepeat(a){
var hash=[],arr=[];
for (var i = 0; i < a.length; i++) {
hash[a[i]]=null;
}
for(var key in hash){
arr.push(key);
}
console.log(arr);
}
outRepeat([2,4,4,5,"a","a"]);//["2", "4", "5", "a"]