How do you move an object from one array to another array by feature?

Question

I am trying to move an object from one array to another. Think of it like adding / moving a friend from non-friend to friend. I have two arrays, which can be seen below, and I am trying to move an object (i.e. a friend) from possible to current via it's 'id'. In the below example, I am trying to move Parker from possible to current with id = 2.

state = {
    current: [
        {
            id: 1,
            name: 'peter'
        }
    ],
    possible: [
        {
            id: 2,
            name: 'parker'
        }
    ]
}


function addFriend(state, action) {
  const { current, possible } = state;
  const addedFriend = Object.assign(
    {},
    state.possible.splice(action.payload.index, 1)
  );

  current.push(addedFriend);

  const newState = { current, possible };
  return newState;
}

Barmar · Accepted Answer · 2019-10-02 22:14:10Z

1

Since you can remove multiple elements with splice(), it returns an array. Index the result to get the specific object. You don't need to use Object.assign(), that just copies the value (which just converts the array into an object whose properties are the array indexes).

var state = {
    current: [
        {
            id: 1,
            name: 'peter'
        }
    ],
    possible: [
        {
            id: 2,
            name: 'parker'
        }
    ]
};

function addFriend(state, action) {
  const { current, possible } = state;
  const addedFriend = state.possible.splice(action.payload.index, 1)[0];

  current.push(addedFriend);

  const newState = { current, possible };
  return newState;
}

state = addFriend(state, {payload: { index: 0 }});
console.log(state);

I'm not sure why you're returning a new state object, since you're modifying the old state in place.

edited Oct 2, 2019 at 22:14

answered Oct 2, 2019 at 22:02

Barmar

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6 Comments

kingloui Over a year ago

Currently current is resulting in: { current: [ { id:1, name: 'peter' }, { 0: { id:2, name: 'parker' } } ] } - i somehow need that 0 to disappear. 1) The reason I am returning new state is because I am using redux, and a don't want to duplicate state. 2) I'm using Object.assign() to try an combat the problem above...

Barmar Over a year ago

I've updated the answer to show how to do it without Object.assign.

Prasanna Over a year ago

@Barmar This works but I think you are mutating the state when you are creating addedFriend variable.

Barmar Over a year ago

current.push() mutates the state, I took that from your original code.

kingloui Over a year ago

how would you do it via id (not via index?)

|

Prasanna · Accepted Answer · 2019-10-02 22:47:30Z

0

It is not that time-efficient if you want a fast running code. But it follows immutability.

We just ignore the item from possible, and add it to current.

state = {
    current: [
        {
            id: 1,
            name: 'peter'
        }
    ],
    possible: [
        {
            id: 2,
            name: 'parker'
        }
    ]
}


function addFriend(state, action) {
  const { current, possible } = state;
  return {
    ...state,
    current: current.concat(possible[action.payload.index]),
    possible: possible.filter((_, index) => index !== action.payload.index)
  }
}

state = addFriend(state, {payload: {index: 0}})
console.log(state)

edited Oct 2, 2019 at 22:47

answered Oct 2, 2019 at 22:38

Prasanna

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