Problem 7/30 of LeetCode 30-day challenge

countElements.js

let countElements = function(arr) {
  // returning a counter of times a number x + 1 
  // is found in an array
  let count = 0;
  // need storage to keep track of x + 1 frequency
  let storage = {};
  
  for(let num of arr){
    // if a number x + 1 is in the array
    if(arr.indexOf(num + 1) > -1) {
      storage[num] = (storage[num] || 0) + 1;
    } 
  }
  
  for(let num of Object.values(storage)){
    count += num;
  }
  
  return count;
};