Javascript - 通过另一个数组中的值在子数组中查找

Question

我有两个 JavaScript 对象:

var classroom = {
  "number" : "1",
    "student" : [ 
      {
        "number" : 1,
        "items" : [ 
          {
            "key" : "00000000000000000000001C",
            "date" : "2016-04-21T17:35:39.997Z"
          }
        ]
      }, 
      {
        "number" : 2,
        "items" : [ 
          {
            "key" : "00000000000000000000001D",
            "date" :"2016-04-21T17:35:39.812Z"
          }, 
          {
            "key" : "00000000000000000000002N",
            "date" :"2016-04-21T17:35:40.159Z"
          }, 
          {
            "key" : "00000000000000000000002Ñ",
            "date" :"2016-04-21T17:35:42.619Z"
          }
        ]
      }
    ],
  }

并且

var items = [ 
  {
    "fields" : {
      "tags" : [ 
        {
          "key" : "00000000000000000000001C",
          "Batch" : "50",
          "Bin" : "01",
          "Tray" : "02"
        }, 
        {
          "key" : "00000000000000000000002N",
          "Batch" : "55",
          "Bin" : "05",
          "Tray" : "12"
        }, 
        {
          "key" : "000000000000228510000032",
          "Batch" : "12",
          "Bin" : "12",
          "Tray" : "01"
        }
      ],
      "Name" : "Rubber"
    },
    "_id" : "56d19b48faa37118109977c0"
  }, 
  {
    "fields" : {
      "tags" : [ 
        {
          "key" : "00000000000000000000001D",
          "Batch" : "50",
          "Bin" : "01",
          "Tray" : "05"
        }, 
        {
          "key" : "00000000000000000000002Ñ",
          "Batch" : "52",
          "Bin" : "07",
          "Tray" : "02"
        }, 
        {
          "key" : "221567010000000000000089",
          "Batch" : "11",
          "Bin" : "15",
          "Tray" : "03"
        }
      ],
      "Name" : "Book"
    },
    "_id" : "56d19b48faa37118109977c1"
  }
];

好的，我需要创建一个函数来遍历 classroom 变量中每个 student 的每个 item。对于每个 item，我需要在 items 数组中找到在其 tags< 之一中具有完全相同 key 的对象.

我的代码得到奇怪的结果...不匹配的项目...

var finalitems = [];

classroom.student.forEach( function (student){
  student.items.forEach( function (obj){

    items.forEach( function (theitem){
      theitem.fields.tags.forEach( function (tag){

        if (tag.key === obj.key) {

          var newitem = theitem;
          newitem.tag = obj;
          finalitems.push(newitem);      
        }
      });
    });         
  });
});

我知道 foreach 是一种指针，但我不太明白为什么它工作得很奇怪以及应该如何完成。

问候，

Answer 1

javascript变量只保存对象引用，而不是内存中的实际对象，所以这一行:

var newitem = theitem;

意味着newitem引用与item相同的对象，而不是从item创建新对象。

所以

newitem.tag = obj;

与

相同

theitem.tag = obj;

这意味着您正在修改输入对象，这就是您无法获得预期输出的原因。

要获得所需的行为，您需要创建该项目的副本并将该对象分配给 newitem 变量:

var newitem = Object.create(theitem);