Several pieces of code to block mouse and keyboard in javascript_javascript skills

//Shield the right mouse button, Ctrl n, shift F10, F5 refresh, backspace key
function KeyDown(){
if ((window.event.altKey)&&
((window.event.keyCode= =37)|| //Shield the Alt direction key ←
(window.event.keyCode==39))){ //Shield the Alt direction key →
alert("You are not allowed to use the ALT direction key to move forward or Back to the web page! ");
event.returnValue=false;
}

/* Note: This is not really blocking the Alt direction key,
because when the Alt direction key pops up a warning box , hold down the Alt key,
click on the warning box with the mouse, this shielding method will be ineffective. In the future,
if any expert has a real way to block the Alt key, please let me know. */

if ((event.keyCode==8) || //Shield the backspace delete key
(event.keyCode==116)|| //Shield the F5 refresh key
( event.ctrlKey && event.keyCode==82)){ //Ctrl R
event.keyCode=0;
event.returnValue=false;
}
if ((event.ctrlKey)&& (event.keyCode==78)) //Shield Ctrl n
event.returnValue=false;
if ((event.shiftKey)&&(event.keyCode==121)) //Shield shift F10
event.returnValue=false;
if (window.event.srcElement.tagName == "A" && window.event.shiftKey)
window.event.returnValue = false; //Shield shift plus left mouse button Open a new webpage
if ((window.event.altKey)&&(window.event.keyCode==115)){ //Block Alt F4
window.showModelessDialog("about:blank","", "dialogWidth:1px;dialogheight:1px");
return false;}
}



function init()
{
try{ announceDiv.innerText = announce; }catch(e){}
}
window.onload=init;