Inventory JS Fundamentals

function inventory(arr) {
    let items = arr.shift().split(', ');
    arr.pop();

    for (let i = 0; i < arr.length; i++) {
      let tokens = arr[i];
      let commands = tokens.split(' - ');
      let command = commands[0];
      let item = commands[1].split(':');
      let oldItem = item[0];
      let newItem = item[1];

      if (command === "Collect") {
        if (!(items.includes(oldItem))) {
          items.push(oldItem);
        }
      } else if (command === "Drop") {
        if ((items.includes(oldItem))) {
          let index = items.indexOf(oldItem);
          if (index !== -1) {
            items.splice(index, 1);
          }
        }
      } else if (command === "Combine Items") {
        if (items.includes(oldItem)) {
          let index = items.indexOf(oldItem);
          if (index !== -1) {
            items.splice(index + 1, 0, newItem)
          }
        }
      } else if (command === "Renew") {
        if (items.includes(oldItem)) {
          let index = items.indexOf(oldItem);
          if (index !== -1) {
            items.splice(index, 1);
            items.push(oldItem);
          }
        }
      }
    }
    console.log(items.join(', '));
}