LeetCode 219. Contains Duplicate II

/**
* @param {number[]} nums
* @param {number} k
* @return {boolean}
*/
var containsNearbyDuplicate = function(nums, k)
{
var hash = {};
for (var i in nums)
{
var index = hash[nums[i]];
for (var j in index)
{
if (Math.abs(i - index[j]) <= k)
{
return true;
}
}
hash[nums[i]] = [i].concat(hash[nums[i]]);
}
return false;
};