How to typehint promises in typescript

[macnibblet]

I currently have the following code

  authenticate(credentials: AuthenticationCredentials): Promise<void> {
    return axios
      .post('backend://authentication', credentials)
      .then<void>(response => {
        this.processToken(response.data.token);
      });
  }

The error it produces

Type 'Promise<void>' is not assignable to type 'Promise<void>'.
  Types of property 'then' are incompatible.
    Type '{ <R1, R2>(onFulfilled: (value: void) => R1 | Promise<R1>, onRejected: (error: any) => R2 | Promi...' is not assignable to type '{ <TResult1, TResult2>(onfulfilled: (value: void) => TResult1 | PromiseLike<TResult1>, onrejected...'.
      Type 'Promise<any>' is not assignable to type 'Promise<any>'.
        Types of property 'then' are incompatible.
          Type '{ <R1, R2>(onFulfilled: (value: any) => R1 | Promise<R1>, onRejected: (error: any) => R2 | Promis...' is not assignable to type '{ <TResult1, TResult2>(onfulfilled: (value: any) => TResult1 | PromiseLike<TResult1>, onrejected:...'.

[croes]

Ran into the same error. The Promise in axios.d.ts (https://github.com/mzabriskie/axios/blob/master/axios.d.ts#L61) seems to be incompatible with the ES6 Promise defined in lib.es6.d.ts (https://github.com/Microsoft/TypeScript/blob/master/lib/lib.es6.d.ts#L1356).

[pmlamotte]

Ran into a similar error that is breaking my vscode setup. My hacky workaround right now was to copy the axios typings locally, remove the promise definition, and reference it through includes in .tsconfig. I then had to manually typecast the return values to make it happy.

axios.post(
    ...
).then(response => response.data as User) as Promise<User>

When I modified the node_modules/axios/axios.d.ts file directly to remove the Promise definition none of that typecasting was necessary since I'm already making use of es2015 promise definitions.

I'm totally new to typescript so I'm not sure what the appropriate fix might be.

[rafaelbiten]

I'm also new to TS and I've been trying to use it on a very small/simple project.

I'm really confused on how to use TypeScript without using 'any' or getting any TS errors/warnings.

I tried many different things, but the image above was probably my best attempt but for some reason I still get the Type 'void' is not assinable to type 'string' error. I was wondering if this could be related to this bug.

If I use (u: string): Axios.IPromise<any>, it fixes the issue, but I'm trying to avoid using 'any'.

Tks!

[DenisCarriere]

If you use async you'll be able to return a Promise<void> from that function, I don't think this issue has anything to do with Axios.

I was able to run this function without any Typescript errors using the default axios.d.ts definition.

async authenticate(credentials: AuthenticationCredentials): Promise<void> {
  const response = await axios.post('backend://authentication')
  this.processToken(response.data.token)
}

[mktange]

This is fixed with the following PR #588

[gluons]

Same here.
Promise from then is not compatible with native Promise.

error TS90010: Type 'Promise<void>' is not assignable to type 'Promise<void>'. Two different types with
 this name exist, but they are unrelated.
  Types of property 'then' are incompatible.

[acheshkov]

+1

[retwedt]

+1 any progress/solutions on this?

[shousper]

+1

[nickuraltsev]

Fixed via 3704d57

[leemove]

It does't work!

[luciomartinez]

This worked for me:

import axios, {AxiosPromise} from 'axios';

function get(): AxiosPromise {
  return axios.get('http://my.domain/api');
}

[vileen]

This worked for me:

import axios, {AxiosPromise} from 'axios';

function get(): AxiosPromise {
  return axios.get('http://my.domain/api');
}

but you don't specify the exact type returned by AxiosResponse so it's any implicitly