I just found another solution using Set(): by copying each element into a new set. Since a set only stores distinct elements, if the number of elements in the input matches the size of the Set, it means there are no duplicates

function containsDuplicate(nums) {
    if(!nums || nums.length == 0){
      return false;
    }
    
    let nums_copy = new Set();

    for(let i = 0; i<nums.length;i++){
      nums_copy.add(nums[i]);
    }

    return nums_copy.size == nums.length ? false:true;
  }