Single number

Script
function singleNumber(nums) {
    let cache = {};
    let arr = [];
    nums.forEach(num => {
      if (cache[num]) {
        cache[num] += 1;
      } else {
        cache[num] = 1;
      }
    })
    for (let key in cache) {
      if (cache[key] === 1) {
        arr.push(key);
      }
    }
    return arr[0];
  }