javascript for loop changes original list variable

Question

I have a collection of objects called the response and I am creating another variable called object that\'s an empty object and creating object.array a

Answer 1

You are just copying them by reference which means they are in the same location in memory so whatever you try to modify one of them the other will get modified in order to prevent this you should pass you in either of these ways:

1. Using Array.from()

object.array = Array.from(response);

2. Using slice()

object.array = response.slice();

3. Using spread syntax (...)

object.array = [...response];

4. Using JSON.parse/JSON.strigify

object.array = JSON.parse(JSON.stringify(response));

But in your particular case, only the last option will work as expected since you got a nested array, you need a deep copy of your element.

So the final result should be something like this:

function runThisLoop() {

  var response = [{
      name: 'Name A',
      age: 2
    },
    {
      name: 'Name B',
      age: 7
    }
  ]


  var object = {}
  object.array = JSON.parse(JSON.stringify(response));

  for (var val of object.array) {
    val.age = null
  }

  console.log("response", response)
  console.log("object.array", object.array)
}

runThisLoop()