Interface Type<T> is an interface which is extending global type Function. I found this in typescript documentation Function about global function.
What does the above code mean? I got this code from angular source code.
export const Type = Function;
export function isType(v: any): v is Type<any> {return typeof v === 'function';}
export interface Type<T> extends Function { new (...args: any[]): T; }
I went through Typescript documentation but not able to figure it out.
The definition
interface Type<T> extends Function { new (...args: any[]): T; }
means that a value of type Type<T> is a function which is also known to be a constructor for instances of type T. Since it extends the Function interface it is a Function, and the syntax { new (⋯): ⋯ } is a construct signature, so it's also a constructor.
That means if you have
declare const f: Type<Date>;
then f is a Function and has all Function's properties like length and bind:
f.apply; // okay
f.call; // okay
f.bind; // okay
f.length; // okay
but it is also a constructor for Date objects:
const d = new f();
// ^? const d: Date;
That being said, I don't know why it's defined this way. All constructor types automatically inherit from Function; you don't need to declare it. You can only use the new operator on functions anyway... classes are just special functions:
class Foo {};
console.log(typeof Foo) // "function"
That means the definition
interface Type<T> { new(...args: any[]): T; }
behaves the same as your version. Perhaps it's defined this way to make the relationship with Function explicit? Not sure. But that's out of scope for the question as asked.