Block the corresponding keyboard button operation

<script language="Javascript">
<!--
  //Block the right mouse button, Ctrl+N, Shift+F10, F11, F5 refresh, backspace key
  //Author: meizz(plum blossom rain) 2002-6-18
function document.oncontextmenu(){event.returnValue=false;}//Block the right mouse button
function window.onhelp(){return false} //Block F1 help
function document.onkeydown()
{
  if ((window.event.altKey)&&
      ((window.event.keyCode==37)||   //Shield Alt+ direction key  please 
       (window.event.keyCode==39)))   //Block Alt+ direction key  - 
  {
     alert(" You are not allowed to use ALT+ Direction key forward or back page! ");
     event.returnValue=false;
  }
     
  if ((event.keyCode==8)  ||                 //Mask the backspace delete key
      (event.keyCode==116)||                 //Mask the F5 refresh key
      (event.ctrlKey && event.keyCode==82)){ //Ctrl + R
     event.keyCode=0;
     event.returnValue=false;
     }
  if (event.keyCode==122){event.keyCode=0;event.returnValue=false;}  //Shielding F11
  if (event.ctrlKey && event.keyCode==78) event.returnValue=false;   //Shielding Ctrl + n
  if (event.shiftKey && event.keyCode==121)event.returnValue=false;  //Shift + F10
  if (window.event.srcElement.tagName == "A" && window.event.shiftKey) 
      window.event.returnValue = false;             //Block shift and left mouse button to open a new page
  if ((window.event.altKey)&&(window.event.keyCode==115))             //Alt + F4
  {
      window.showModelessDialog("about:blank","","dialogWidth:1px;dialogheight:1px");
      return false;
  }
}
-->
</script>