Javascript 数组值在循环内未定义

Question

我正在尝试比较两个对象。如果在 savedList 中也找到了 checkedList 中的项目，我想从 checkedList 中复制数组中的第一项，并将其与找到的项目放在 savedList 中。如果在 savedList 中找不到 checkedList 中的项目，我想将整个项目添加到 savedList。我不想在 savedList 中两次保留相同的项目。我正在使用 pop/push 方法来执行此操作。

我运行遇到的问题是在 [ while->for 循环] 中。

未捕获类型错误：无法读取未定义的属性（读取“1”） 当在 savedList 中找到一个项目时，我希望进行必要的更改，然后通过 pop() 移动到下一个项目。然而，当我使用 pop() 方法时，前一项丢失了。下面是我的工作代码以及 link 到 JSFiddle.

期望输出：

savedItemList = {
    "listName": "List_daily:Daily Get From Back List",
    "date": "",
    "itemList": [
      [  11, 888 ], [  55, 227 ],  [  44, 236 ],
      [  3, 700 ],  [  2, 600 ]
    ]
};

var savedItemList = {
    "listName": "List_daily:Daily Get From Back List",
    "date": "",
    //itemList contains [item quantity, item ID]
    "itemList": [
      [  1, 888 ], [  2, 227 ],  [  3, 236 ],
      [  3, 700 ],  [  2, 600 ]
    ]
};

var checkedItemList = [
    //itemData contains [item quantity, item ID]
    { "rowNumber": 1,  "itemData": [ 11, 888 ]  },
    { "rowNumber": 4,  "itemData": [ 44, 236 ]  },
    { "rowNumber": 3,  "itemData": [ 55,  227]  }
];

function moveItemsToList(savedItemList, checkedItemList)
{
  //while checkedItemList length is not zero
     while(checkedItemList.length)
     {
     //pop the last element inside checkedList
         var temp = checkedItemList.pop().itemData;
     //loop through the items inside savedList
     for(let k=0; k < savedItemList.itemList.length; k++)
        {
      //compare temp[1] itemID with savedList itemID
            if(temp[1] == savedItemList.itemList[k][1])
            {
        //if found save the quantity from temp[0] variable to savedItemList 
                savedItemList.itemList[k][0] = temp[0];
        //then move onto the next item on checkedList
                temp = checkedItemList.pop();
            }
        }
     //if items from CheckedList not Found in savedList        //Add the item and its quantity to savedList
        savedItemList.itemList.push(temp);
            
     }
     console.log(savedItemList);    
     
}

moveItemsToList(savedItemList, checkedItemList);

Answer 1

使用现代 JavaScript 数组方法。

const savedItemList = {
    "listName": "List_daily:Daily Get From Back List",
    "date": "",
    //itemList contains [item quantity, item ID]
    "itemList": [
      [  1, 888 ], [  2, 227 ],  [  3, 236 ],
      [  3, 700 ],  [  2, 600 ]
    ]
};

const checkedItemList = [
    //itemData contains [item quantity, item ID]
    { "rowNumber": 1,  "itemData": [ 11, 888 ]  },
    { "rowNumber": 4,  "itemData": [ 44, 236 ]  },
    { "rowNumber": 3,  "itemData": [ 55,  227]  }
];

function moveCheckedToSaved(savedItemList, checkedItemList) {
  checkedItemList.forEach((checkedItem) => {
    const itemID = checkedItem.itemData[1]
    const dupeIndex = findDuplicate(itemID, savedItemList)
    if (dupeIndex !== -1) {
      savedItemList[dupeIndex][0] = checkedItem.itemData[0]
    } else {
      savedItemList.push(checkedItem.itemData)
    }
  })
}

function findDuplicate(id, list) {
  return list.findIndex(item => item[1] === id)
}

moveCheckedToSaved(savedItemList.itemList, checkedItemList)
document.write(savedItemList.itemList.join(' '))

Answer 2

我假设您想将数据保存在 checkedItemList 中，因为您说过 copy。下面的代码解决了你的问题，但是我重写了整个函数。

var savedItemList = {
    "listName": "List_daily:Daily Get From Back List",
    "date": "",
    //itemList contains [item quantity, item ID]
    "itemList": [
      [  1, 888 ], [  2, 227 ],  [  3, 236 ],
      [  3, 700 ],  [  2, 600 ]
    ]
};

var checkedItemList = [
    //itemData contains [item quantity, item ID]
    { "rowNumber": 1,  "itemData": [ 11, 888 ]  },
    { "rowNumber": 4,  "itemData": [ 44, 236 ]  },
    { "rowNumber": 3,  "itemData": [ 55,  227]  }
];

function moveItemsToList(savedItemList, checkedItemList){
  
  //loop through checkItemList with checkedItem as the currently looped object
  for(let checkedItem of checkedItemList){
    itemData = checkedItem.itemData; //itemData is "itemData": [ quantity, ID ]"

    //loop through savedItemList.itemList with savedItem as the currently looped array
    for(let savedItem of savedItemList.itemList){

      //check if the IDs between checkedItemList.itemData and savedItemList.itemList matched
      if(itemData[1] === savedItem[1]){

        //delete the matched data from savedItemList.itemList and break the savedItemList.itemList loop
        savedItemList.itemList.splice(savedItemList.itemList.indexOf(savedItem), 1);
        break;
      }
    }

    //add new data to savedItemList.itemList
    itemDataToBeAdded = itemData;
    savedItemList.itemList.push(itemDataToBeAdded);
  }
  console.log(savedItemList);
}

moveItemsToList(savedItemList, checkedItemList);

编辑：将 for in 循环替换为 for of 循环，因为 for in 已弃用

Javascript 数组值在循环内未定义

Javascript array value is undefined inside loop

javascript

arrays

push

object