/**
 * @param {number[]} nums
 * @return {boolean}
 */
var containsDuplicate = function (nums) {
  const hash = nums.reduce((acc, cur) => {
    acc[cur] = (acc[cur] || 0) + 1;
    return acc;
  }, {});
  return Object.values(hash).some(v => v > 1);
};

console.log(containsDuplicate([1, 2, 3, 1]));

/**
 * @param {number[]} nums
 * @return {boolean}
 */
 var containsDuplicate = function(nums) {
    return (new Set(nums)).size !== nums.length
    
};