Definitelytyped: [@types/lodash] Property 'map' does not exist on type FunctionChain<any>

Created on 21 May 2019 · 8Comments · Source: DefinitelyTyped/DefinitelyTyped

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- Authors: @aj-r @sandersn

One more similar to https://github.com/DefinitelyTyped/DefinitelyTyped/issues/35400 issue (ts is in strick mode):

chain([1, 2, 3, 4, 5])
  .reduce((acc: any, x) => {
    acc[x] = x
    return acc
  }, {})
  .map(x => x * 2)
  .value()

with @types/lodash 4.14.121 it works fine, but with 4.14.126 I get a type error:

 Property 'map' does not exist on type 'FunctionChain<any> | ObjectChain<any> | PrimitiveChain<any> | StringChain | (CollectionChain<any> & FunctionChain<any> & ObjectChain<any> & PrimitiveChain<any> & StringChain) | StringNullableChain | CollectionChain<...>'.
  Property 'map' does not exist on type 'FunctionChain<any>'.

Obviously map function is exist here in any case and this is incorrect error.

Update: Same issue happens with mapValues after reduce too

Source

EugeneDraitsev

👍4

Most helpful comment

where you guys able to figured out this issue?

alvarezr on 5 May 2020

👍4

All 8 comments

I think the types are having trouble with the acc: any part. It might be possible to fix but I'm not sure.

You can probably give a stricter type than any, e.g. (acc: { [key: string]: any }, x) => .... That should fix the error, and has the added benefit of being more type-safe.

aj-r on 22 May 2019

@aj-r, you're right it will work as expected with more strict type:

interface MyInterface { [key: string]: any }

chain([1, 2, 3, 4, 5])
  .reduce((acc: MyInterface, x) => {
    acc[x] = x
    return acc
  }, {} as MyInterface)
  .map(x => x * 2)
  .value()

But error

 Property 'map' does not exist on type 'FunctionChain<any> | ObjectChain<any> | PrimitiveChain<any> | StringChain | (CollectionChain<any> & FunctionChain<any> & ObjectChain<any> & PrimitiveChain<any> & StringChain) | StringNullableChain | CollectionChain<...>'.
  Property 'map' does not exist on type 'FunctionChain<any>'.

still doesn't make any sense. In case of acc: any you still have property map on your FunctionChain<any>. At least this is incorrect error message.

EugeneDraitsev on 22 May 2019

The problem is that reduce returns acc, and when acc: any, it can't guarantee that it does have the map method. It might be a function, for example, which doesn't have map. You should either add a type to acc or not put a type annotation at all (which is a noImplicitAny error, but fine without strict on).

sandersn on 22 May 2019

You're right acc might be a string, number or function, but map always exists at Chain<any>:

const { chain } = require('lodash')

const fn = chain([1, 2, 3, 4, 5])
  .reduce(() => () => {})

const num = chain([1, 2, 3, 4, 5])
  .reduce(() => 42)

const str = chain([1, 2, 3, 4, 5])
  .reduce(() => 'string')


console.log(fn.map) // [Function]
console.log(num.map) // [Function]
console.log(str.map) // [Function]

So maybe semantically this error make sense, but this error get wrong information to end users.

Edit: Moreover any type means that any.map is exist or at least missing of this property is not an error from types point of view.

EugeneDraitsev on 22 May 2019

@aj-r @sandersn, any updates about that? If my points are not enough here, so here is 1 more unsolvable point:

interface Token {
  [key: string]: any
}

chain(decodedToken as Token).get('[cognito:groups]').map(decodeGroup).orderBy().value()

There is no any way to fix that, except ugly any-wrapper:
```tsx
(chain(decodedToken as Token).get('[cognito:groups]') as any).map(decodeGroup).orderBy().value()

map, mapValues and get should exist at ObjectChain<any> | PrimitiveChain<any>. Otherwise meaning of any has no any sense here.

EugeneDraitsev on 4 Jun 2019

👍2

I use the lodash(4.17.11) and the different @types/lodash(4.14.118 and 4.14.136), the 4.14.118 is worked, but the 4.14.136 is showing the error.