Why delete it's working in another variable?

Question

Why delete is working in another data ?

      this.Line = [];
      this.showDataForm = [{
        'name': 'BTC',
        'data': [1,2,3,4]
        'chart': 'linemulti'
      }]

      for (var index=0; index < this.showDataForm.length; index++) {
        if ( this.showDataForm[index].chart === "linemulti" ) { // for merge chart
          this.Line.push(this.showDataForm[index]);
        }
      }
      
      for (var key=0; key < this.Line.length; key++){
          delete this.Line[key].chart;
      }

I try to show:

console.log(this.showDataForm);

[{'name':'BTC','data':[1,2,3,4]}]

why delete is working in this.showDataForm ? how to fix ?

You're referencing the same object when you delete and when you console.log — Jamiec, Sep 30 '20 at 07:20
No I delete this.Line `delete this.Line[key].chart;` but it's delete this.showDataForm. — user14324808, Sep 30 '20 at 07:27

Jamiec · Accepted Answer · 2020-09-30T07:50:56.960

When you call delete on the item in the Line array, it is just a reference to the original object in showDataForm.

If you wanted to instead copy a new item to the Line array you can use the spread operator ... as is shown below. This means the original object is not affected when you delete one of the keys:

this.Line = [];
this.showDataForm = [{
  'name': 'BTC',
  'data': [1,2,3,4],
  'chart': 'linemulti'
}]

for (var index=0; index < this.showDataForm.length; index++) {
  if ( this.showDataForm[index].chart === "linemulti" ) { // for merge chart
    this.Line.push({...this.showDataForm[index]});
  }
}

for (var key=0; key < this.Line.length; key++){
    delete this.Line[key].chart;
}

console.log(this.showDataForm)

Why delete it's working in another variable?

1 Answers1