Creating objects dynamically and self unreferencing

guys. I'm making an endless runner in which I need some objects to come from the top of the screen and then get destroyed once they're no longer visible.

Screenshot of how it looks like right now

I created the class "banana":

function Banana() {
    this.height = 1.96;
    this.width = 3.955;
    this.pos_x = 300;
    this.pos_y = -30;
    this.banana_image = new Image();
    this.banana_image.src = 'img/banana.png';
};

And a Move function:

Banana.prototype.move = function(){
    if (this.pos_y > 500) {
        //destroy it
        this.constructor = undefined; //????
    }
    this.height += 0.5;
    this.width += 0.5;
    this.pos_y += 5;
    this.pos_x -= 2.2;
};

I created the object in my Game.Initialize function, but it only runs once so it doesn't really help me.

I want to be able to create them dynamically on my Game.update. I was thinking about using an array of objects, but since I'm new to Javascript I don't know how it would work.