Keylistener in Javascript

Question

I'm looking for a KeyListener for a game I'm developing in JavaScript. I have no idea how this would work in real code but it would be something like this:

if(keyPress == upKey)
{
    playerSpriteX += 10;
}
else if(keyPress == downKey)
{
    playerSpriteY -= 10;
} 

etc...

I searched it up, and Google came up with things that involved AJAX which I don't understand yet. Is there a built in function in JavaScript that does this?

Answer 1

Here's an update for modern browsers in 2019

let playerSpriteX = 0;

document.addEventListener('keyup', (e) => {
  if (e.code === "ArrowUp")        playerSpriteX += 10
  else if (e.code === "ArrowDown") playerSpriteX -= 10

  document.getElementById('test').innerHTML = 'playerSpriteX = ' + playerSpriteX;
});

Click on this window to focus it, and hit keys up and down
<br><br><br>
<div id="test">playerSpriteX = 0</div>

---

Original answer from 2013

window.onkeyup = function(e) {
   var key = e.keyCode ? e.keyCode : e.which;

   if (key == 38) {
       playerSpriteX += 10;
   }else if (key == 40) {
       playerSpriteX -= 10;
   }
}

FIDDLE