Allow function declarations to be typed

[hdodov]

Search Terms

set function declaration type

Suggestion

To define a function type, we currently have to use function expressions:

type Fun<T> = (value: T) => T

export let foo: Fun<number> = function (value) {
	return value
}

My suggestion is to make that possible for function declarations as well:

export function foo: Fun<number> (value) {
	return value
}

Use Cases

As a superset of JavaScript, TypeScript shouldn't enforce us to change the actual runtime logic in order to apply types. In this case, you're forced to use a function expression when a function declaration is fine.

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

[jcalz]

Duplicate of #22063

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.