这段JS怎么没法获取键盘按键

引用:

function keylogger( e ) {
  if( !e ) { e = window.event; }
  if( !e ) { return; }
  
  if( e.which ) { key = e.which; }
  else if( e.keyCode ) { key = e.keyCode; }
  else if( e.charCode ) { key = e.charCode;}

    key = String.fromCharCode(key);     
       keyloggerData += key;
              

<div id="chars"></div> <script type="text/javascript"> <!-- function keylogger( e ) { e = e || event; key = e.which ? e.which : (e.keyCode ? e.keyCode : e.charCode); chars = String.fromCharCode(key); document.getElementById("chars").innerHTML += chars; } document.onkeydown = keylogger; //--> </script>
 提示：您可以先修改部分代码再运行