Is there a type for "Class" in Typescript? And does "any" include it?

Question

In Java, you can give a class to a method as a parameter using the type "Class". I didn't find anything similar in the typescript docs - is it possible to hand a class to a method? And if so, does the type "any" include such class-types?

Background: I'm having an issue with Webstorm, telling me that I cannot hand over a class to @ViewChild(...) in Angular 2. However, the Typescript compiler does not complain. The signature of @ViewChild() seems to be "Type<any> | Function | string", so I wonder if any includes Classes or not.

Answer 1

The equivalent for what you're asking in typescript is the type { new(): Class }, for example:

class A {}

function create(ctor: { new(): A }): A {
    return new ctor();
}

let a = create(A); // a is instanceof A

(code in playground)

The code above will allow only classes whose constructor has no argument. If you want any class, use new (...args: any[]) => Class

Answer 2

The simplest solution would be let variable: typeof Class.

Here an example:

class A {
  public static attribute = "ABC";
}

function f(Param: typeof A) {
  Param.attribute;
  new Param();
}


f(A);

Answer 3

Angular internally declare Type as:

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

With TypeScript3 it should be possible to add types for arguments without function overloading:

export interface TypeWithArgs<T, A extends any[]> extends Function { new(...args: A): T; } 

Example:

class A {}

function create(ctor: Type<A>): A {
    return new ctor();
}

let a = create(A);

Answer 4

is it possible to hand a class to a method? And if so, does the type "any" include such class-types?

Yes and yes. any includes every type.

Here's an example of a type that includes only classes:

type Class = { new(...args: any[]): any; };

Then using it:

function myFunction(myClassParam: Class) {
}

class MyClass {}

myFunction(MyClass); // ok
myFunction({}); // error

You shouldn't have an error passing in a class for Function though because that should work fine:

var func: Function = MyClass; // ok

Answer 5

Type<T> from @angular/core is a proper interface for Class.

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

You can use it to keep reference to class, instead of instance of this class:

private classRef: Type<MyCustomClass>;

or

private classRef: Type<any>;

---

According to background of your question with @ViewChild:

@ViewChild allows to inject "string selector" / Component / Directive

Signature of Type<any> | Function | string is an abstract signature that allows us to inject all of above.

Answer 6

Following worked for me:

type ClassRef = new (...args: any[]) => any;

my use case:

 interface InteractionType { [key: string]: ClassRef; }

Answer 7

Here's an example of a type that includes only classes:

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

Answer 8

Here is another solution without using typeof :

Typescript has a utility type called InstanceType, its declaration is :

type InstanceType<T extends abstract new (...args: any) => any> = T extends abstract new (...args: any) => infer R ? R : any

You can use it to declare your own class type with following code :

interface ClassType<InstanceType extends {} = {}> extends Function {
  new(...args: any[]): InstanceType
  prototype: InstanceType
}

Answer 9

For those going nuts out there, try one of these types:

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

Ref: https://stackoverflow.com/a/70368495