javascript - Movement for out-of-bound objects, canvas -

i have space ship in canvas. has velocities, ship.vx , ship.vy. when it's 30px away canvas borders set ship.vx & ship.vy 0 , move background objects in ship's opposite direction. @ moment ship stuck @ point. that's good. if try move left-right(stuck @ top/bottom) or top-down(stuck @ left/right) doesn't since stuck in point vx & vy set 0.

if accelerate in it's opposite direction takes 5 seconds pick it's velocity (around 2), it's @ same point 5 seconds.

i tried not set vy 0 when out of x-axis , vice-versa ship keeps moving in other axis.

so i'm trying achieve ship'll stuck when it's 30 px border, if try move or accelerate in other 3 directions it'll pretend if it's not stuck.

any of know mechanisms?
thanks.

function stuckship(){     if(                 (ship.x - ship.width < 0)  ||                  (ship.x + ship.width > w)  ||                 (ship.y + ship.height > h) ||                 (ship.y - ship.height < 0))               {         ship.vx = 0;         ship.vy = 0;      }  }   function againandagain(){     var angle = ship.rotation;      var x = math.cos(angle);     var y = math.sin(angle);              var ax = x*thrust,         ay = y*thrust;      ship.vx += ax;     ship.vy += ay;              stuckship();             ship.draw(context);  }  document.addeventlistener('keydown', function(e){     switch(e.keycode){         case 38:             thrust = 0.35;         break;         case 37:             ship.rotation -= 3;         break;         case 39:             ship.rotation += 3;         break;       } } 

manipulating velocity of object based on it's position on screen display-purposes never best idea. use parent-based systems, have 1 main-container , objects (including ship) child container , move relatively main-container. can update container's position, if ship's global position in 30px-band, make "lock" on edge of screen.