Contains Duplicate

LeetCode題目: 217. Contains Duplicate

My solution:

/**
 * @param {number[]} nums
 * @return {boolean}
 */
let containsDuplicate = nums => {
    let map = new Map();
    for(let i=0; i<nums.length; i++) {
        if(map.has(nums[i])) return true
        else map.set(nums[i], 1);
    }
    return false;
};