在 Javascript 上使用 addEventListener 时 keydown 不起作用

Question

I am trying to use "keydown" as getEventListener in my little canvas game.But it downst work; I am just trying to move my object with keydown.

<script>
var tuval = document.getElementById("tuval");
var cizim = tuval.getContext("2d");
tuval.addEventListener('keydown',keypress);
function keypress(e){
    if (e.keyCode === 37){
    dx = dx * -1;}
}
var en = tuval.width;
var boy = tuval.height;
var x = en/2;
var y = boy/2;
var dx = 2;
var dy = 4;
function ziplayantop() {
  temizle();
  cizim.beginPath();
  cizim.arc(x,y,10,0,2*Math.PI);
  cizim.closePath();
  cizim.fillStyle="#ff0000";
  x = x + dx;
  y = y + dy;
  cizim.fill();
  if (x>en-5||x < 0 ) {
      dx = -1 * dx;
  }
  if (y>boy-5||y < 0) {
    dy = -1 * dy;
  }
  if (tiklama) {
    dx = -1 * dx;
    dy = -1 * dy;
  }
}
function temizle(){
  cizim.beginPath();
  cizim.fillStyle="#ffffff";
  cizim.fillRect(0,0,tuval.width,tuval.height);
  cizim.closePath();
  cizim.fill();
}
setInterval(ziplayantop,50);
</script>

It works when i replace "keydown" with "clik" like this way;

tuval.addEventListener('click',keypress);

function keypress(){
    dx = dx * -1;
}

Could you please help me on this? Thanks

Answer 1

be informed that you can't bind keydow directly to the canvas..bind it to the entire window instead

window.addEventListener("keydown", function, false);