TypeScript type declaration for promise.prototype.finally signature

Question

TypeScript type declaration for promise.prototype.finally signature

I recently came across a ES6 Promise compatible finally implementation called promise.prototype.finally that I was using in a Node application. Now, I want to convert this application to TypeScript but unfortunately, I couldn't find any typings available for this package on DefinitelyTyped. In situations like these, I have created my own impromptu type definitions for the functionality that I require. However, given that this library modifies the prototype of the Promise object, I am unsure about how to represent it conventionally in TypeScript. Any suggestions or ideas?

Possibly related:

https://github.com/Microsoft/TypeScript/issues/280
https://github.com/Microsoft/TypeScript/issues/7015
https://github.com/Microsoft/TypeScript/issues/6722
Declaration merging with ES6 style modules

typescript es6-promise definitelytyped

Answer 1

Answer №1

Slava's response is accurate, but it only addresses typing the finally block. To effectively integrate the shim into your code so that you can utilize p.finally(() => { ... }), you must execute the shim.

~~Regrettably, the typings on DefinitelyTyped currently do not support the shim function. Therefore, until this is rectified, it is recommended to manually incorporate the typings.~~

~~declare interface Promise<T> { finally(onFinally?: () => U | Promise): Promise; } declare module 'promise.prototype.finally' { export function shim(): void; }~~

The typings are now accessible. To install, use

npm install --save-dev @types/promise.prototype.finally

Within your TypeScript code, when initializing the application, call

import { shim } from 'promise.prototype.finally';
shim();

This action will implement the finally block in the Promise prototype, allowing usage of the finally feature as needed.

Answer 2

Slava's response is accurate, but it only addresses typing the finally block. To effectively integrate the shim into your code so that you can utilize p.finally(() => { ... }), you must execute the shim.

~~Regrettably, the typings on DefinitelyTyped currently do not support the shim function. Therefore, until this is rectified, it is recommended to manually incorporate the typings.~~

~~declare interface Promise<T> { finally(onFinally?: () => U | Promise): Promise; } declare module 'promise.prototype.finally' { export function shim(): void; }~~

The typings are now accessible. To install, use

npm install --save-dev @types/promise.prototype.finally

Within your TypeScript code, when initializing the application, call

import { shim } from 'promise.prototype.finally';
shim();

This action will implement the finally block in the Promise prototype, allowing usage of the finally feature as needed.

Answer 3

Answer №2

If you're looking to implement this without any shims, it's now possible with TypeScript 2.7. Keep in mind that as of February 26th, 2018, TS 2.7 is not fully ES2018 compatible yet. Although there are some things still missing, like Promise.finally which was added in the 2.7 release. While tsconfig-schema accepts ES2018 as a target, TS 2.7 doesn't have complete knowledge of ES2018. To access new features like Promise.finally in TypeScript 2.7, make sure to set your "target": "ESNEXT" in your tsconfig.json.

With this setup, you can write code similar to the following:

myAsyncFunction().then
(
  (var) => console.log("executing then. " + var)
)
.catch
(
  (var) => console.log("executing catch. " + var)
)
.finally
(
  () => console.log("executing finally.")
)

It's important to note that finally won't accept any arguments due to its nature.

Remember: although TypeScript transpiles correctly and understands your code, always verify if your JS engine supports Promise.finally. In my case, using NodeJs 8.x resulted in non-executable JS since Promise.Finally is only supported from Node 10.x onwards, check this link for more details.

Answer 4

If you're looking to implement this without any shims, it's now possible with TypeScript 2.7. Keep in mind that as of February 26th, 2018, TS 2.7 is not fully ES2018 compatible yet. Although there are some things still missing, like Promise.finally which was added in the 2.7 release. While tsconfig-schema accepts ES2018 as a target, TS 2.7 doesn't have complete knowledge of ES2018. To access new features like Promise.finally in TypeScript 2.7, make sure to set your "target": "ESNEXT" in your tsconfig.json.

With this setup, you can write code similar to the following:

myAsyncFunction().then
(
  (var) => console.log("executing then. " + var)
)
.catch
(
  (var) => console.log("executing catch. " + var)
)
.finally
(
  () => console.log("executing finally.")
)

It's important to note that finally won't accept any arguments due to its nature.

Remember: although TypeScript transpiles correctly and understands your code, always verify if your JS engine supports Promise.finally. In my case, using NodeJs 8.x resulted in non-executable JS since Promise.Finally is only supported from Node 10.x onwards, check this link for more details.

Answer 5

Answer №3

If you want to customize your TypeScript types, you can create your own d.ts file and reference it in the tsconfig.json configuration file. This way, you can contribute your custom definitions to the DefinitelyTyped repository for the benefit of others.

Update:

To extend the existing Promise class in your own d.ts file, you can make specific methods optional so as not to conflict with the original implementation. Ensure that you define the extension as an interface within your d.ts file.

Your custom d.ts file might resemble this:

declare module 'es6-promise/dist/es6-promise' {
    export interface Promise <R> {
      finally?<U>(onFinally?: () => U | Promise<U>): Promise<U>;
    }
}

With these modifications, everything should function correctly...

I have provided an example project to showcase this: promise-typescript-extension-demo

A pull request has been submitted to the DefinitelyTyped repository, so hopefully, it will be approved soon, allowing you to access the updated definitions from there...

Answer 6

If you want to customize your TypeScript types, you can create your own d.ts file and reference it in the tsconfig.json configuration file. This way, you can contribute your custom definitions to the DefinitelyTyped repository for the benefit of others.

Update:

To extend the existing Promise class in your own d.ts file, you can make specific methods optional so as not to conflict with the original implementation. Ensure that you define the extension as an interface within your d.ts file.

Your custom d.ts file might resemble this:

declare module 'es6-promise/dist/es6-promise' {
    export interface Promise <R> {
      finally?<U>(onFinally?: () => U | Promise<U>): Promise<U>;
    }
}

With these modifications, everything should function correctly...

I have provided an example project to showcase this: promise-typescript-extension-demo

A pull request has been submitted to the DefinitelyTyped repository, so hopefully, it will be approved soon, allowing you to access the updated definitions from there...

TypeScript type declaration for promise.prototype.finally signature

Answer №1

Answer №2

Answer №3

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