Scratch

import flash.events.KeyboardEvent;
import flash.ui.Keyboard;

stage.addEventListener(KeyboardEvent.KEY_DOWN, fire);

function fire(evt:KeyboardEvent):void
{
    if (evt.keyCode == Keyboard.SPACE)
    {
        var laser:bullet = new bullet;
        stage.addChild(laser);
        laser.x = player.x + player.width / 2;
        laser.y = player.y;
        while (laser.y > 0)
        {
            laser.y += 5;
        }
        stage.removeChild(laser);
    }
}