用JS实现一个数组合并的方法（要求去重）

Array.prototype.unique = function(){
var a = {};
for(var i = 0; i < this.length; i++){
if(typeof a[this[i]] == "undefined")
a[this[i]] = 1;
}
this.length = 0;
for(var i in a)
this[this.length] = i;
return this;
}
var a = [1,2,3];
var b = [2,3,4];
var c = a.concat(b).unique();

Array.prototype.unique2 = function(){
var a = {},
b = {},
n = this.length;
for(var i = 0; i < n; i++){
if(typeof(b[this[i]]) != "undefined")
continue;
if(typeof(a[this[i]]) == "undefined"){
a[this[i]] = 1;
}else{
b[this[i]] = 1;
delete a[this[i]];
}
}
this.length = 0;
for(var i in a)
this[this.length] = i;
return this;
}
var a = [1,2,3,4];
var b = [2,3,5,7];
var d = a.concat(b).unique2();