how to make a copy of object in javascript/vuejs

This question already has an answer here:

How do I correctly clone a JavaScript object? 54 answers

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You are not creating a copy. You are assigning the reference to this.items to your itemsCopy array. Thus, you are later mutating the same array.

Create a copy with:

itemsCopy = this.items.slice();

The same issue applies with each object inside your array. In your loop, create a copy of the object:

var obj = Object.assign({}, itemsCopy[i]);
obj.text = "something";
itemsCopy[i] = obj;  //replace the old obj with the new modified one.

---

Demo:

var items = [
  {text: 'text1', active: true},
  {text: 'text1', active: true},
  {text: 'text1', active: true}
];

function copyAndChange() {
  var itemsCopy = []
  itemsCopy = items.slice();
  for (var i=0; i<itemsCopy.length; i++) {
    var obj = Object.assign({}, itemsCopy[i]);
    obj.text = "something";
    itemsCopy[i] = obj;  //replace the old obj with the new modified one.
    console.log('text from items: ' + items[i].text)
    console.log('text from itemsCopy: ' + itemsCopy[i].text)
  }
  return itemsCopy
}

copyAndChange();

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