Store Provision

function solve(arr1, arr2) {
  let currentStock = turnIntoObject(arr1);
  let newStock = turnIntoObject(arr2);

  Object.keys(newStock).forEach((el) => {
    if (!currentStock[el]) {
      currentStock[el] = newStock[el];
    } else {
      currentStock[el] += newStock[el];
    }
  });

  Object.keys(currentStock).forEach(key => console.log(`${key} -> ${currentStock[key]}`));

  function turnIntoObject(arr) {
    let obj = {};
    for (let i = 0; i < arr.length; i += 2) {
      obj[arr[i]] = Number(arr[i + 1]);
    }
    return obj;
  }
}