获取数组中出现次数最多的元素

function duplicates(arr) {
var obj = {},
keys = [],
values = [];
arr.forEach(function(item){
if(obj[item]){
obj[item] = obj[item]+1;
}else{
obj[item] = 1;
}
});
for(key in obj){
keys.push(key);
values.push(obj[key]);
}
var max= Math.max.apply(Math,values),
idx = values.indexOf(max);
return keys[idx];
}