Tips for ensuring the correct function type in TypeScript

Question

Tips for ensuring the correct function type in TypeScript

TypeScript Version 3.5.1

I've encountered an issue with TypeScript where the compiler fails to flag missing arguments in function declarations. Here's a basic illustration of the problem.

interface IArgs {
  foo: number;
}

type MyFunc = (args: IArgs) => Promise<any>;

// No complaint from TypeScript about missing arguments here
const fn: MyFunc = async() => { };

/*
Uncommenting the line below will make the TypeScript compiler complain,
but it should have caught the issue in the previous declaration.
*/

// fn();

How can I prompt the TypeScript compiler to detect and alert me about missing arguments in function definitions?

typescript

Answer 1

Answer №1

Interesting point!

In my opinion, typescript deliberately made this design choice.

While it's valid to opt not to use arguments in a function, it is not acceptable to leave out arguments when calling a function.

Consider a click handler as an example:

type ClickHandler = (evt: MouseEvent) => any

// Examples of valid usage:
element.onClick = () => doSomething()
element.onClick = (evt) => doSomething(evt.target.value)

Because some ClickHandler functions might require the argument while others may not, it must always be provided.

const fn: ClickHandler = () => {}
fn() // results in a Typescript error

Answer 2

Interesting point!

In my opinion, typescript deliberately made this design choice.

While it's valid to opt not to use arguments in a function, it is not acceptable to leave out arguments when calling a function.

Consider a click handler as an example:

type ClickHandler = (evt: MouseEvent) => any

// Examples of valid usage:
element.onClick = () => doSomething()
element.onClick = (evt) => doSomething(evt.target.value)

Because some ClickHandler functions might require the argument while others may not, it must always be provided.

const fn: ClickHandler = () => {}
fn() // results in a Typescript error

Tips for ensuring the correct function type in TypeScript

Answer №1

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