Utility type - "Instantiable"

[jlachniet]

Suggestion

🔍 Search Terms

instantiable, utility type

✅ 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

When writing a TypeScript decorator, it's useful to have a type representing any function or class that can be instantiated. This can be described using a custom type like:

type Instantiable = new (...args: never) => unknown;

This allows you describe an instantiable function or class without resorting to any or unknown. I think that including this utility type as part of the built in TypeScript types would be helpful.

📃 Motivating Example

I created a library a while ago can serialize instances of classes. I wrote a Serializable decorator that registers classes for serialization. The decorator needs to access target.prototype which doesn't work if target is unknown.

type Instantiable = new (...args: never) => unknown;

function Serializable(identifier: string) {
	return (target: Instantiable) => register(target.prototype, identifier);
}

💻 Use Cases

The easiest solution is just to declare your own Instantiable type. You can also use unknown or any, which are less than ideal.

[RyanCavanaugh]

We don't add utility types to the library unless they're required for declaration emit

See also https://twitter.com/SeaRyanC/status/1540022633344905216, #39522 (comment)

[typescript-bot]

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