How to overwrite the first array with the second one?

Question

Here's the arrays:

const firstArr = [
  {
    id: 1,
    code: '1'
  },
  {
    id: 2,
    code: '2'
  },
  {
    id: 3,
    code: '3'
  },
]

const secondArr = [
  {
    id: 1,
    code: '1',
    bool: true,
  },
  {
    id: 2,
    code: '2',
    bool: true,
  },
]

Desired result is:

const overwrittenArr = [
  {
    id: 1,
    code: '1',
    bool: true,
  },
  {
    id: 2,
    code: '2',
    bool: true,
  },
  {
    id: 3,
    code: '3'
  },
]

secondArr should overwrite the firstArr by the code value, if it's exact the same value as in the firstArr, then it should be replaced with the object from the secondArr. I've tried to do that with filter, but had no success.

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score 1 · Accepted Answer · answered Jun 30 '21 at 18:11

1

You could use forEach in order to mutate the first array like this:

const firstArr = [
  {
    id: 1,
    code: '1'
  },
  {
    id: 2,
    code: '2'
  },
  {
    id: 3,
    code: '3'
  },
]

const secondArr = [
  {
    id: 1,
    code: '1',
    bool: true,
  },
  {
    id: 2,
    code: '2',
    bool: true,
  },
]

secondArr.forEach(x => Object.assign(firstArr.find(y => y.id === x.id) || {}, x))

console.log(firstArr)

answered Jun 30 '21 at 18:11

Guerric P

30,447
6
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That's interesting way to use `Object.assign`, so it is the optimal way on achieving this? – Alexander Kim Jun 30 '21 at 18:14
I guess it is, if you don't mind overriding potential conflicting properties between the two objects – Guerric P Jun 30 '21 at 18:15

score 0 · Answer 2 · answered Jun 30 '21 at 18:14

0

You could assign the second array to the first.

const
    firstArr = [{ id: 1, code: '1' }, { id: 2, code: '2' }, { id: 3, code: '3' }],
    secondArr = [{ id: 1, code: '1', bool: true }, { id: 2, code: '2', bool: true }];

Object.assign(firstArr, secondArr);

console.log(firstArr);

.as-console-wrapper { max-height: 100% !important; top: 0; }

answered Jun 30 '21 at 18:14

Nina Scholz

376,160
25
347
392

Dupe, dupe dupe. Including your answers too – mplungjan Jun 30 '21 at 18:15
Works because the items are sorted, the secondArr is shorter, there are no missing ids, and same object properties except `bool` – Guerric P Jun 30 '21 at 18:20

score 0 · Answer 3 · answered Jun 30 '21 at 18:30

Object.assign to the rescue!

const firstArr = [
  {
    id: 1,
    code: '1'
  },
  {
    id: 2,
    code: '2'
  },
  {
    id: 3,
    code: '3'
  },
];

const secondArr = [
  {
    id: 1,
    code: '1',
    bool: true,
  },
  {
    id: 2,
    code: '2',
    bool: true,
  },
];

const overwrittenArr = [
  {
    id: 1,
    code: '1',
    bool: true,
  },
  {
    id: 2,
    code: '2',
    bool: true,
  },
  {
    id: 3,
    code: '3'
  },
];

let result = Object.assign(firstArr, secondArr);

alert(JSON.stringify(result) === JSON.stringify(overwrittenArr));

How to overwrite the first array with the second one?

3 Answers3