How to determine if object is array-like and convert it into array?

Question

I'm using dep-object-diff, which returns differences between two objects.

The problem is that if I have something like,

const objectA = {
  fieldA: 5,
  fieldB: ['123']
}
const objectB = {
  fieldA: 5,
  fieldB: ['123', '456']
}

Then it returns,

const diff = {
  fieldB: {
    0: '456'
  }
}

When the required response object should be,

const diff = {
  fieldB: ['456']
}

How can I detect if diff.fieldB is an array (dynamically, without hardcoding), and consequently convert it into one?

Edit

Thanks to @Nina Scholz, I ended up using her approach as the base. The problem which I caught with my data, however, was that the approach didn't work for strings. Anyway, I ended up implementing it as follows:

const diffs = {
  fieldA: "SOME_STRING",
  fieldB: {
    3: '123',
    5: '456'
  },
};

const chronologize = (object) => {
  let counter = 0;

  for (let prop in object) {
    if (object[prop]) {
      object[counter] = object[prop];
      delete object[prop];
      counter++;
    }
  }

  return object;
};

const result = Object.fromEntries(
  Object.entries(diffs).map(([k, v]) =>
    typeof v === 'string'
      ? [k, v]
      : [k, Object.assign([], chronologize(v))]),
);

console.log(result);

Well, the object may contain properties the have values that are arrays or strings. Your answer worked brilliantly for the use case I posted, but sometimes the diff object can be const diff = { fieldA: 10, fieldB: { 3: '456' } }, where fieldB.length === 4. This means that fieldA changed and that fieldB also changed -- the change in fieldB being an addition of an element to the array. I worked around this, however, using your approach as a base. I had to do several more transformations, such as making sure it's { 0: '456' } and not { 3: '456' }, but that's ok, I think. — Mike K
– Mike K, Commented Apr 16, 2020 at 12:18

Nina Scholz · Accepted Answer · 2020-04-16 07:34:10Z

1

You could get the entries, convert the array like object to array with Object.assign and an array as target and convert back to an object.

const 
    diff = { fieldB: { 0: '456' } },
    result = Object.fromEntries(Object.entries(diff).map(([k, v]) => [k, Object.assign([], v)]));

console.log(result);

answered Apr 16, 2020 at 7:34

Nina Scholz

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2 Comments

Mike K Over a year ago

Hello, sorry, I know this wasn't asked, but what if it's const diff = { fieldA: 'someString', fieldB: { 0: '456' } }?

Nina Scholz Over a year ago

the result is funny, you get single letters for a string value.

{   "fieldA": [     "s",     "o",     "m",     "e",     "S",     "t",     "r",     "i",     "n",     "g"   ],   "fieldB": [     "456"   ] }

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