Javascript when holding down arrow keys?

Question

I have this script to trigger some javascript. But the script does not support holding down the arrow keys. How can I make this work when I hold the arrow keys.

document.onkeyup = KeyCheck;       
function KeyCheck()
{
    var KeyID = event.keyCode;

    switch(KeyID)
    {
      case 37:
      right('img'); document.getElementById('img').src = 'guyl.png';
      break;
      
      case 38:
      up('img');
      break

      case 39:
      left('img'); document.getElementById('img').src = 'guyr.png';
      break;

      case 40:
      down('img');
      break;   
     }
}

Answer 1

should be:

document.onkeydown = KeyCheck;

onkeypress : invokes JavaScript code when a key is pressed

onkeydown : invokes JavaScript code when a key is held down (but not yet released)

onkeyup : invokes JavaScript code when a key is has been released after being pressed.