Is the return type of 'void' being overlooked in TypeScript - a solution to avoid unresolved promises?

When working in TypeScript 3.9.7, the compiler is not concerned with the following code:

const someFn: () => void = () => 123;

After stumbling upon this answer, it became apparent that this behavior is intentional. The rationale behind it makes sense (essentially, ignoring the return type when passing the function as an argument).

However, things take a turn when dealing with promises:

const someFn: () => void = () =>
  new Promise((resolve, reject) => reject(Error('onoez')));
someFn();

I am using ESLint's 

@typescript-eslint/no-floating-promises
rule to catch unhandled promise rejections in my code. In the example above, since the linter believes someFn does not have a return value, it will not issue a warning.

Do I just have to accept this situation? If a function expects a () => void type callback and I provide it with an async function, the compiler won't flag any issues, leading to potential problems. Is there a way to prevent this?

typescriptpromiseeslintvoid

Answer №1

When a function has a return type of void in TypeScript, it means that the return value cannot be used, regardless of what it is. However, this does not prevent the function from actually returning something. This behavior will remain unchanged.

The syntax () => void indicates that you do not need to know or use the return value because it is not important for your purpose. But in some cases, such as this one, the return value does matter.

To enforce that a function does not return any value at all, you can use a return type of undefined.

const someFn: () => undefined = () =>
  // Type 'Promise<unknown>' is not assignable to type 'undefined'.
  new Promise((resolve, reject) => reject(Error('oh no!')));

Similar questions

If you have not found the answer to your question or you are interested in this topic, then look at other similar questions below or use the search

Forwarding parameter data type

I am facing an issue with 2 navigation points leading to the same screen 1. this.router.navigate([this.config.AppTree.App.Module.Details.Path], { state: { data: { id: this.TableId } } }); this.router.navigate([this.config.AppTree.App.Module.Details.Pa ...

angulartypescriptangular-routing

Angular button for opening or closing the menu that redirects the page to a localhost URL

I have implemented a template from the link below into my project. So far, everything has been working fine, but recently I noticed that the menu open/close button is malfunctioning. Whenever I click on the close button while on any page (for example, http ...

angulartypescript

Error message encountered following the removal of an undesirable type from an array in Typescript

When working with TypeScript, I am facing an issue. I have an array defined as Array<string|undefined, and my goal is to filter out the undefined values from this array and assign the resulting array to a variable of type Array<string>. However, I ...

typescript

Utilizing a Map with Angular's ngFor

Currently, I am working with Ionic 3, which utilizes Angular and TypeScript. My goal is to use ngFor with a Map type in my project. Below is what I have implemented so far: interface IShared_Position { lat: number; lng: number; time: number; ...

angulartypescriptngforiterable

The functionality of verifying the type of an item in a list using Typescript is not functioning

In my TypeScript code, I am working with a type called NameValue and another one called MixedStuff. type NameValue = { name: string; value: string }; type MixedStuff = NameValue | string; function stripTwoChars(stuffs: MixedStuff[]): string { let st ...

typescript

Encountered issue when attempting to insert items into the list in EventInput array within FullCalendar and Angular

I am struggling to create a dynamic object that I need to frame and then pass to the FullCalendar event input. Here is my initial object: import { EventInput } from '@fullcalendar/core'; ... events: EventInput[]; this.events = [ { title: &ap ...

angulartypescriptfullcalendar

The issue of circular dependencies in TypeScript arises specifically within the Record type rather than in an ordinary object type

Can you explain the difference between two types, where one throws a TS error and the other does not? type ScopeItem = | string | { all: string; team: string; }; type ScopesTree = Record<string, ScopeItem | Record& ...

typescript

Mocking a third-party callback function in Jest for method implementation

Utilizing Nest + Cognito for user authentication in an application, I have a method within my Authentication service that requires testing/mocking: async cognitoRegister(userPool: CognitoUserPool, { name, password, email }: AuthRegisterInput): ...

javascripttypescriptunit-testingjestjsnestjs

The deployment of the remix is unsuccessful in Vercel, even though it functions perfectly during development. The error message states that 'AbortController' is not

I'm new to React and could use some assistance with a deployment issue on Vercel. Any ideas on why this is failing? I haven't explicitly used AbortController anywhere, so I'm suspecting it might be related to one of the installed packages? ...

typescriptvercelremix.run

Is there a way for me to retrieve the callback parameters?

Can the parameters of the callback function be accessed within the 'outer' function? function f(callback: (par1: string)=>void): void { // Is it possible to access 'par1' here? } ...

typescript

Is there a way for me to add a clickable link within a tooltip?

In my title, I want to insert a clickable link like 'Link' or 'a'. The title is ready for any string you input. <MaterialSwitch title={CLICKABLE STRING HERE} /> ...

javascriptreactjstypescript

Stop the ion-fab-list from automatically closing when an element is selected within it

I'm having trouble getting a form to stay visible when a fab is clicked in my Ionic 4 app. Every time I click on a fab or another component within the ion-fab-list, the ion-fab-list automatically closes. How can I prevent this from happening and keep ...

angulartypescriptionic-frameworkionic4angular8

Error 404 when implementing routing in Angular 2 with Auth0

In my Angular 2 application, I am utilizing Auth0 authentication. While everything works fine on localhost, I encounter issues when running the application on the server (my domain). Based on what I know, my problem seems to be with the routes. Iss ...

angularauthenticationtypescriptauth0

Preventing the automatic selection of the initial item in a PrimeNG dropdown menu

While utilizing the p-menu component from PrimeNG in popup mode ([popup]="true"), I encountered an unexpected issue where the first item in the menu is automatically selected and turns gray. Here is the code snippet that I am using: <p-menu #menu [popu ...

htmlcssangulartypescriptprimeng

Guide on importing an external JavaScript library in Node.js utilizing a TypeScript declaration file

I am working on a Node.js project using Typescript and I am facing an issue with integrating mime.js (https://github.com/broofa/node-mime). Even though I have a declaration file available (https://github.com/borisyankov/DefinitelyTyped/blob/master/mime/mim ...

javascriptnode.jstypescript

typescript: How to restrict an array's type in a specific order

Is there a way to restrict the types of elements in an array in TypeScript without specifying paradigms? For example, instead of defining arrays as follows: const arr:Array<any> = [] I would like to be able to specify a specific order for the arr ...

arraystypescriptdefinitions

What is the reason behind installing both Typescript and Javascript in Next.js?

After executing the command npx create-next-app --typescript --example with-tailwindcss my_project, my project ends up having this appearance: https://i.stack.imgur.com/yXEFK.png Is there a way to set up Next.js with Typescript and Tailwind CSS without i ...

javascriptreactjstypescriptnext.js

Jodit-React: Addressing the Placeholder Problem

I've recently incorporated Jodit-react into my react-typescript project, but I encountered an error when adding the config property. The error message stated that it "Has no property common with type." Unfortunately, I'm unsure why this is happe ...

reactjstypescriptjodit

Mismatch between generic types

When working with this code, I encounter a syntax error at m1 and m2. The error message states: Type 'T' is not assignable to Type 'boolean' or Type 'T' is not assignable to Type 'string' interface customMethod { ...

typescript

In Typescript, an interface is defined where the "id" property is required to be a number, while all other properties must be of

I am in need of creating an interface to represent data received from the server, where the id is a number and all other properties are strings. This is what I attempted: interface AnyChartsData { id: number; [key: string]: string; } However, I enco ...

typescript