数组去重

利用数组中的reduce方法，push方法，和for循环

function flatten(a1,a2){
var result =[];
var arr = [];

arr = a2.reduce(function(prev,curr){
prev.push(curr);
return prev;
},a1);

for (var i = 0; i < arr.length; i++) {
var index = arr[i];
if (result.indexOf(index) === -1) {
result.push(index);
}
}

return result;

}

flatten([2,3,4],[6,9,3,4]);   //[2, 3, 4, 6, 9]