Typescript - Cannot list methods over an Object

Question

I have a class like this:

export class A {

    @Decorator()
    public a(): void {
        ...
    }

    @Decorator()
    public b(): void {
        ...
    }

}

Later, having an instance of A (passed in as an Object though), I want to list all its methods. I thought that Reflect.ownKeys( aInstance: Object ) could give me what I wanted, but the resulting array coming from the function is empty. What am I doing wrong?

Answer 1

That's because in javascript the methods are part of the prototype of the constructor.

It's easier to see why if you look at the compiled javascript, for example this:

class A {
    public a(): void {}

    public b(): void {}
}

Compiles to:

var A = (function () {
    function A() {
    }
    A.prototype.a = function () { };
    A.prototype.b = function () { };
    return A;
}());

So:

let a = new A();
console.log(Object.keys(a)); // []
console.log(Object.keys(a.constructor.prototype)); // ["a", "b"]
console.log(Object.keys(A.prototype)); // ["a", "b"]