Problem 1/30 of LeetCode 30-day challenge

singleNumber.js

let singleNumber = function(nums) {
    // frequency counter way
    let freq = {};
    let lonely;
  
    // iterate thru array
    for(let num of nums){
        // if num does not exist as key,
        // create it or increment otherwise
        if(!freq[num]){
            freq[num] = 1;
        } else {
          freq[num] = (freq[num] || 0) + 1;
        }
    }
    // Find key (num) with val === 1
    for(let key in freq){
        if(freq[key] === 1) {
            lonely = parseInt(key); 
        }
    }

    
  // return that number
  return lonely;
};