Javascript:for循环中的 map 总是返回最后一项

Question

我正在尝试修改对象数组，并在 for 循环内使用映射。我的实现似乎总是返回 map 中的最后一项。

代码:

let testArray = [
    {
        body: 'test sentence',
        uid: "a"
    },
    {
        body: 'Another test sentence',
        uid: "b"
    }
]

var allItems = []
for (var item of testArray) {
    let splittedBody = item.body.split(' ')

    let splittedArray = splittedBody.map((word, i) => {
        item.body = word
        item.objectID = `${item.uid}:${i}`
        return item
    })
    allItems.push(splittedArray)
}

allItems = Array.prototype.concat(...allItems)
console.log(allItems)

上面的代码打印以下内容:

[ { body: 'sentence', uid: 'a', objectID: 'a:1' },
  { body: 'sentence', uid: 'a', objectID: 'a:1' },
  { body: 'sentence', uid: 'b', objectID: 'b:2' },
  { body: 'sentence', uid: 'b', objectID: 'b:2' },
  { body: 'sentence', uid: 'b', objectID: 'b:2' } ]

我想要的是:

[ { body: 'test', uid: 'a', objectID: 'a:0' },
  { body: 'sentence', uid: 'a', objectID: 'a:1' },
  { body: 'Another', uid: 'b', objectID: 'b:0' },
  { body: 'test', uid: 'b', objectID: 'b:1' },
  { body: 'sentence', uid: 'b', objectID: 'b:2' } ]

编辑:理想情况下，我不想在映射函数中构造另一个项目，因为 testArray 中的每个对象可能具有其他对象中不存在的属性。在 map 函数中构造另一个项目意味着我必须检查这些属性中的 undefined ，这很容易出错。

Answer 1

您的问题来自于您对 item 所做的阴影:

let testArray = [{
    body: 'test sentence',
    uid: "a"
  },
  {
    body: 'Another test sentence',
    uid: "b"
  }
]

var allItems = []
for (var item of testArray) {
  let splittedBody = item.body.split(' ')

  let splittedArray = splittedBody.map((word, i) => {

    // Create a clone of item -> don't use item
    var itemClone = JSON.parse(JSON.stringify(item)); 
    
    itemClone.body = word
    itemClone.objectID = `${item.uid}:${i}`
    return itemClone       // <-- return the modified clone
  })
  allItems.push(splittedArray)
}

allItems = Array.prototype.concat(...allItems)
console.log(allItems)

item 在 for 循环中声明:

for (var item of testArray) {

但是你实际上修改了正文和其中的 objectID:

    let splittedArray = splittedBody.map((word, i) => {
        item.body = word
        item.objectID = `${item.uid}:${i}`