Immutable.js Push into array in nested object

Question

Assume there is an object:

const object = {
  'foo': {
    'bar': [1, 2, 3]
  }
}

I need to push 4 to object.foo.bar array.

Right now I'm doing it like this:

const initialState = Immutable.fromJS(object)
const newState = initialState.setIn(
  ['foo', 'bar', object.foo.bar.length],
  4
)
console.log(newState.toJS())

But I don't really like it, since I need to use object.foo.bar.length in the path. In my real example object is nested much deeper, and getting array's length looks very ugly. Is there another, more convenient way?

Derek Adair · Accepted Answer · 2019-04-16 16:16:45Z

41

This should work

initialState.updateIn(['foo', 'bar'], arr => arr.push(4))

References:

https://immutable-js.github.io/immutable-js/docs/#/updateIn

edited Apr 16, 2019 at 16:16

Derek Adair

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answered Jul 27, 2016 at 10:27

zerkms

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4 Comments

Alexandr Lazarev Over a year ago

Great! Thanks a lot!

Derek Adair Over a year ago

arr.push is wrong, as it returns the /length/ of the new array. This will result in {foo: { bar: 3}}. You want to use arr.concat

Steve Klösters Over a year ago

arr.push is correct here but the naming is a little misleading: arr in his example is Immutable's List because OP created the state through Immutable.fromJS. List.push returns a new list with the argument(s) appended, so this does exactly what OP asked.

zerkms Over a year ago

@PabloCG you're wrong, push here is not a Array.prototype method, but an immutablejs List method, which DOES NOT modify the original object.

Huy Nguyen · Accepted Answer · 2017-08-14 07:42:40Z

9

I'm using seamless-immutable, when I'm adding a new item to array of nested object, I got this error:

The push method cannot be invoked on an Immutable data structure.

My array still has push method, but it doesn't work. The solution is use concat instead, more details on #43:

initialState.updateIn(['foo', 'bar'], arr => arr.concat([4]));

Hope this help!

answered Aug 14, 2017 at 7:42

Huy Nguyen

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1 Comment

Lucas Over a year ago

Same issue here, makes sense since push modifies which isn't possible with immutable data structures.

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