Armrest Assembly for Vehicle and Door Assembly Having Slidable Armrest for Vehicle

A door assembly includes a door panel including a metallic plate material, a lower trim attached to the door panel, and an armrest installed on top of the lower trim and configured to be slidable in a longitudinal direction of a vehicle. The door assembly further includes a base fixedly installed on the top of the lower trim, a slider positioned on top of the base, wherein the armrest is coupled to a top of the slider, and a guide fixedly installed on the base and configured to penetrate the slider.