POS - adding a new product

Hi I am working with a module in a pos module and I want to do something. I am creating a button in a pos orderline and I want when this button is clicked it should add another product automatically as the product already selected with the same quantity.

i could get already selected product information like id, name, etc., but i don't know how to add a new one using this button

I hope someone can tell me where is the function that adds a new order or product to the order line, so I can send him the line

like this:

var line = this.pos.get('selectedOrder').getLastOrderline();