Javascript keydown spacebar + cursor keys

Question

I'm having a problem with getting an input from cursor keys on a keydown event. I am using a keydown event for spacebar and the arrow keydown event at the same time (in a spaceinvaders game, you should be able to move AND fire via spacebar at the same time).

The ship should be able to move along the x and y axis at the same time while spacebar is pressed. Now the actual problem: whenever spacebar is pressed to fire, I can move up and forward, but not forward and down. I also can move backwards and down but not backwards and up. when the spacebar is not pressed it works and I can move diagonally. The same applies for wasd keys.

    if (e.keyCode == 37 || e.keyCode == 38 || e.keyCode == 39 || e.keyCode == 40) 
    e.preventDefault();

       if (e.keyCode == 32){
             e.preventDefault();
             spaceState = true;
       }

       if (e.keyCode == 87 || e.keyCode == 38) keyState["UpDown"]="w";//w
       if (e.keyCode == 83 || e.keyCode == 40) keyState["UpDown"]="s";//s

       if (e.keyCode == 65 || e.keyCode == 37) keyState["RightLeft"]="a";//a
       if (e.keyCode == 68 || e.keyCode == 39) keyState["RightLeft"]="d"; //d

combination w and d works combination s and a works

w,a and s,d DONT work

Still all combinations work when spacebar is not pressed, wasd combinations work even when the spacebar is returning a keydown event. The question simply is why?

Answer 1

I answered a very similar question recently so I'm going to just copy my answer from there.

Odds are this is nothing to do with your code. Many keyboards, to save cost, are not capable of supporting every combination of 3 or more keys at once, and are specifically wired to support combinations that are in common use (such as Ctrl+Alt+Del). The phenomenon is known as "ghosting".

See this page from Microsoft for an expanded explanation.