function() implements () => unknown {}

[DanieliusDev]

Suggestion

🔍 Search Terms

function implements

✅ Viability 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, new syntax sugar for JS, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

⭐ Suggestion

Allow to add a implements Type for a function (not arrow functions). This would allow to easily use a function type on a non-arrow function.

📃 Motivating Example

export default function Component(props) implements React.FC {
    // ...
}

💻 Use Cases

Usually whenever we want to use a function type from a library such as react, we tend to do one of the two things:

• add the argument and return types ourselves
• create a new variable for a function with most likely an arrow function

This isn't awful to have to deal with but most people prefer using function instead of arrow functions whenever declaring a function which is not a call-back for a function. Another problem is that we can't type a function whenever using export.

Here is how we currently make and export a function:

const Component: React.FC = (props) => {
    // ...
}

export default Component;

or

export default function Component(props: {}): React.ReactElement<any, any> {
    // ...
}

Here is how it could be done:

export default function Component(props) implements React.FC {
    // ...
}

[IllusionMH]

Duplicate of #22063 and other similar proposals

[DanieliusDev]

Duplicate of #22063 and other similar proposals

5 years ago and still no implementation....

[RyanCavanaugh]

Wait until you hear how long there have been feature suggestions in C++!