javascript each overwrite array object

Question

This is my code

$(function() {
  var sqlTable = [
    {
      name: 'a',
      TagName: 'a_1'
    },
    {
      name: 'b',
      TagName: 'b_1'
    }
  ];

  var hbaseTable = [
    {
      TagName: 'a_12015',
      Tvalue: '1'
    },
    {
      TagName: 'a_12016',
      Tvalue: '2'
    },
    {
      TagName: 'b_12015',
      Tvalue: '1'
    },
    {
      TagName: 'b_12016',
      Tvalue: '3'
    }
  ];

  var new_result = temp(sqlTable, hbaseTable);

  function temp(a, b) {
    var new_result2 = [];
    var k = 0;

    for (var i=0; i<a.length; i++) {
      var sql_value = a[i];
      var tag_name = sql_value.TagName;

      for (var j=0; j<b.length; j++) {
        var hbase_value = b[j];
        var hbase_tag = hbase_value.TagName;
        var hbase_tvalue = '';
        var hbase_tag_name = '';

        console.log('/', hbase_tag + ', ' + tag_name);
        if (hbase_tag.indexOf(tag_name) > -1)
        {
          var t_sql_value = sql_value;
          hbase_tvalue = hbase_value.Tvalue;
          hbase_tag_name = hbase_value.TagName;
          t_sql_value.hbase_tvalue = hbase_tvalue;
          t_sql_value.hbase_tag_name = hbase_tag_name;
          new_result2.push(t_sql_value);
          k++;
        }
      }
    }

    return new_result2;
  }

  console.log('new_result', new_result);
});

I want result is

0: Object
  TagName: "a_1"
  hbase_tag_name: "a_12016"
  hbase_tvalue: "1"
  name: "a"
__proto__: Object
1: Object
  TagName: "a_1"
  hbase_tag_name: "a_12016"
  hbase_tvalue: "2"
  name: "a"
__proto__: Object
2: Object
  TagName: "b_1"
  hbase_tag_name: "b_12016"
  hbase_tvalue: "1"
  name: "b"
__proto__: Object
3: Object
  TagName: "b_1"
  hbase_tag_name: "b_12016"
  hbase_tvalue: "3"
  name: "b"

but I alway get the result is

0: Object
  TagName: "a_1"
  hbase_tag_name: "a_12016"
  hbase_tvalue: "2"
  name: "a"
__proto__: Object
1: Object
  TagName: "a_1"
  hbase_tag_name: "a_12016"
  hbase_tvalue: "2"
  name: "a"
__proto__: Object
2: Object
  TagName: "b_1"
  hbase_tag_name: "b_12016"
  hbase_tvalue: "3"
  name: "b"
__proto__: Object
3: Object
  TagName: "b_1"
  hbase_tag_name: "b_12016"
  hbase_tvalue: "3"
  name: "b"

This is my JSFiddle

I believe it's because objects are reference variables. So b[j] will hold last value. — Rajesh Dixit
– Rajesh Dixit, Commented Nov 14, 2015 at 5:46

André Chalella · Accepted Answer · 2015-11-14 06:15:44Z

The problem is that you think you're cloning an object when you're in fact just creating a new reference to the same object in the two highlighted lines below:

  function temp(a, b) {
    var new_result2 = [];
    var k = 0;

    for (var i=0; i<a.length; i++) {
      var sql_value = a[i];                 ////////// ERROR 1
      var tag_name = sql_value.TagName;

      for (var j=0; j<b.length; j++) {
        var hbase_value = b[j];
        var hbase_tag = hbase_value.TagName;
        var hbase_tvalue = '';
        var hbase_tag_name = '';

        console.log('/', hbase_tag + ', ' + tag_name);
        if (hbase_tag.indexOf(tag_name) > -1)
        {
          var t_sql_value = sql_value;      ////////// ERROR 2
          hbase_tvalue = hbase_value.Tvalue;
          hbase_tag_name = hbase_value.TagName;
          t_sql_value.hbase_tvalue = hbase_tvalue;
          t_sql_value.hbase_tag_name = hbase_tag_name;
          new_result2.push(t_sql_value);
          k++;
        }
      }
    }

    return new_result2;
  }

If you inspect sqlTable after your original code runs, you'll see it's badly defaced by your function.

To solve the problem, really clone by changing each of the lines above for:

var sql_value = { name: a[i].name, TagName: a[i].TagName };             // ERROR 1
var t_sql_value = { name: sql_value.name, TagName: sql_value.TagName }; // ERROR 2

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