Inventory Update (advanced algorithms)

function updateInventory(arr1, arr2) {
//   var newArr = [];
  
//   Reverse array values so that the the 
//   first values are the names instead of amounts
  arr1 = reverseArrayValues(arr1);
  arr2 = reverseArrayValues(arr2);
  
  console.log("BEFORE\narr1: "+ arr1 + "\narr2: "+arr2);
  
  // if old array has value from new array
  // set the value to the sum of both 
  // the sum of both values
  for (var updated in arr2) {
    for (var old in arr1) {
      if (arr1[old].indexOf(arr2[updated][0]) !== -1) {
        arr1[old][1] += arr2[updated][1];
      } else {
        arr1.push(arr2[updated]);
      }
    }
  }

   console.log("AFTER\narr1: "+ arr1 );
  
  
    return false;
  
   
}

function reverseArrayValues(arr) {
    var reversed = arr.reduce(function(all, item) {
      all.push([item[1], item[0]]);
      return all;
    },[]);
    
    
    //return reversed;
  }


updateInventory([[21, "Bowling Ball"], [2, "Dirty Sock"], 
                 [1, "Hair Pin"], [5, "Microphone"]],
                
                [[2, "Hair Pin"], [3, "Half-Eaten Apple"], 
                 [67, "Bowling Ball"], [7, "Toothpaste"]]);