Javascript - Finding in subarray by value from another array

Question

I have two javascript objects:

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"
          }
        ]
      }
    ],
  }

AND

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"
  }
];

Ok, I need to create a function that goes through every item of every student in classroom variable. With each item, I need to find in the items array the object that has the exact same key in one of its tags.

My code is getting strange results...missmatching items...

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);      
        }
      });
    });         
  });
});

I know that foreach is a kind of a pointer but I don't really understand why it is working strange and how it should be done.

Regards,

jsfiddle.net/ynqtjL3d Please, find that the tag of each item is not what it should be. I can see 4 items (correct) but there are two items with tag key "00000000000000000000002Ñ" and another two with tag key "00000000000000000000002N" when there should be 4 items but each one with a different tag key (00000000000000000000001C,00000000000000000000001D,00000000000000000000002N,00000000000000000000002Ñ) — Egidi
– Egidi, Commented Apr 21, 2016 at 18:42

WorldFS · Accepted Answer · 2016-04-21 18:45:46Z

2

javascript variables only save object references, not the actual object in memory, so this line:

var newitem = theitem;

means newitem refers to the same object as theitem, NOT create a new object from theitem.

so

newitem.tag = obj;

is the same as

theitem.tag = obj;

Which means you're modifying the input objects, that's why you won't get the expected output.

To get the desired behavior you need to create a copy of theitem and assign that object to newitem variable:

var newitem = Object.create(theitem);

answered Apr 21, 2016 at 18:45

WorldFS

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Comments

Nina Scholz · Accepted Answer · 2016-04-21 18:55:28Z

Maybe this helps with a lot more iterations.

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" }] }] },
    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" }],
    finalitems = [];

classroom.student.forEach(function (student) {
    student.items.forEach(function (studentItem) {
        items.forEach(function (item) {
            item.fields.tags.forEach(function (itemTag) {
                if (itemTag.key === studentItem.key) {
                    finalitems.push({
                        key: studentItem.key,
                        date: studentItem.date,
                        Batch: itemTag.Batch,
                        Bin: itemTag.Bin,
                        Tray: itemTag.Tray,
                    });
                }
            });
        });
    });
});
document.write('<pre>' + JSON.stringify(finalitems, 0, 4) + '</pre>');

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