Introduce Class or Constructor utility type

[DanKing123]

🔍 Search Terms

Class Constructor utility type

✅ Viability Checklist

• 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 our Design Goals: https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals

⭐ Suggestion

Angular includes a Type utility type which is defined like this:

export declare interface Type<T> extends Function {
    new (...args: any[]): T;
}

I think this could be more succinctly defined, and I think the word "Type" here is a little misleading, as this actually denotes a class/constructor.

I'm wondering though, why TypeScript doesn't have a built-in equivalent? (Or if it does, why I can't find it, and it isn't documented here: https://www.typescriptlang.org/docs/handbook/utility-types.html)

I was thinking something like this:

export type Constructor<T> = new(...args: any[]) => T;

or maybe even:

export type Class<T> = new(...args: any[]) => T;

It's easy enough to hand-roll, but just feels like something that ought to be built into the language?

📃 Motivating Example

This pattern is already used extensively in many on-line code examples. E.g. see here: https://dev.to/kalashin1/utility-types-in-typescript-4nfo - although this post suggests TypeScript already has this feature, whereas as far as I can tell, it actually doesn't!

💻 Use Cases

I've used the Angular Type utility type quite extensively in my Angular application, whenever I want to pass around classes for some reason, whilst also keeping track of their associated instance types.

[MartinJohns]

The team decided against adding more utility types, unless they're needed for emit purposes. There's even a PR that will add "not a request for a utility type" to the viability checklist: #55746

And of course there's already #26990, #54428, #20256 and many more. Used search terms: constructor type in:title

[typescript-bot]

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