Within the realm of JavaScript, every function possesses a unique property recognized as the prototype. When a function is utilized as a constructor (by invoking it with new), the resulting instance will inherit this property. This mechanism mirrors how classes operated in JavaScript prior to ES2015:
// Class in ES5 flavor
function Foo() { } // A standard function
Foo.prototype.prop = 0; // Adding a property to Foo.prototype
var f = new Foo(); // Utilizing Foo as a constructor
f.prop; // The instance inherits the added property
With the introduction of ES2015, the class syntax was implemented, functioning equivalently beneath the surface. Hence, constructor objects retain a prototype property from which their instances inherit:
// Class in ES2015 flavor
class Foo { } // Explicitly declared as a class
Foo.prototype.prop = 0; // Adding a property to Foo.prototype
const f = new Foo(); // Using Foo as a constructor
f.prop; // The instance inherits the added property
When translated into TypeScript, it is stated that the Function interface, integral to all functions, includes a prototype property of any type. Moreover, when employing the class syntax, the constructor is still recognized as a Function, and the prototype property of the constructor is narrowed down to the identical type as the constructed instance of the class:
// TypeScript code
class Foo {
prop!: number; // Foo possesses a prop
}
Foo.prototype; // Identified as type Foo
Foo.prototype.prop = 0; // Facilitated due to the prior context
const f = new Foo(); // Identified as type Foo
f.prop; // Identified as type number
Even when delving into abstract classes in TypeScript, a prototype property bearing the same type as the instance type is evident. Despite the impossibility of utilizing new on an abstract class constructor or aligning it with a newable type such as new() => any, the prototype remains a viable subject of discussion:
// Further TypeScript code
abstract class Bar {
abstract prop: number;
}
Bar.prototype; // Examined as type Bar
Bar.prototype.prop = 0; // Progress attained via this line
const b = new Bar(); // Regrettably, this operation is unfeasible
Consequently, in TypeScript, a conceivably-abstract class constructor is considered (a subtype of) a Function that incorporates a prototype property indicating the instance type. Thus, the declaration:
type PossiblyAbstractConstructor<T> = Function & {prototype: T};
Upholds the combination of Function and "object with a prototype property of type T" through the intersection operator...
Alternatively, the interface definition:
interface PossiblyAbstractConstructor<T> extends Function {
prototype: T;
}
Accomplishes the same outcome via interface extension...
Thus, the following remains a valid statement:
const fooConstructor: PossiblyAbstractConstructor<Foo> = Foo;
const barConstructor: PossiblyAbstractConstructor<Bar> = Bar;
This elucidates the relevance of the answer to the original query. Best of luck!