get properties of a Class using Typescript

Is there a way to get properties names of class in TypeScript: in the example I would like to 'describe' the class A or any class and get an array of its properties (maybe only public one ? ), is it possible? or should I instantiate the object first?

 class A {
    private a1;
    private a2;
    /** Getters and Setters */

}

 class Describer<E> {
    toBeDescribed:E ;
    describe(): Array<string> {
        /**
         * Do something with 'toBeDescribed'                          
         */
        return ['a1', 'a2']; //<- Example
    }
}

let describer = new Describer<A>();
let x= describer.describe();
/** x should be ['a1', 'a2'] */