Disable backspace key sample code

I want to share a javascript to disable the backspace key with you.
As you know, when the mouse cursor fouse on a non-input field such as white space, radio button,
button and you press the backspace key, the page will go back to previous page.
The script is disable this feature but the backspace key still works when mouse cursor focus in a input text field.
It works in IE7 and Firefox3.0.

<script language="JavaScript1.2">
// Every single key press action will call this function.
function shouldCancelBackspace(e) {
   var key;
   if(e){ 
  key = e.which? e.which : e.keyCode;
  if(key == null ¦¦ ( key != 8 && key != 13)){ // return when the key is not backspace key.    
    return false;
  }
   }else{
     return false;
   }
if (e.srcElement) { // in IE
tag = e.srcElement.tagName.toUpperCase();
type = e.srcElement.type;
readOnly =e.srcElement.readOnly;
if( type == null){ // Type is null means the mouse focus on a non-form field. Disable     backspace button
  return true;
}else{
  type = e.srcElement.type.toUpperCase();
}
} else { // in FF
tag = e.target.nodeName.toUpperCase();
type = (e.target.type) ? e.target.type.toUpperCase() : "";
}
// we don't want to cancel the keypress (ever) if we are in an input/text area
if ( tag == 'INPUT' ¦¦ type == 'TEXT' ¦¦type == 'TEXTAREA') { 
 if(readOnly == true ) // if the field has been dsabled, disbale the back space button
       return true;
 if( ((tag == 'INPUT' && type == 'RADIO') ¦¦ (tag == 'INPUT' && type == 'CHECKBOX'))
   && (key == 8 ¦¦ key == 13) ){
  return true;  // the mouse is on the radio button/checkbox, disbale the backspace button
 }
  return false; 
}
// if we are not in one of the above things, then we want to cancel (true) if backspace
return (key == 8 ¦¦ key == 13);
}
// check the browser type
function whichBrs() {
var agt=navigator.userAgent.toLowerCase();
if (agt.indexOf("opera") != -1) return 'Opera';
if (agt.indexOf("staroffice") != -1) return 'Star Office';
if (agt.indexOf("webtv") != -1) return 'WebTV';
if (agt.indexOf("beonex") != -1) return 'Beonex';
if (agt.indexOf("chimera") != -1) return 'Chimera';
if (agt.indexOf("netpositive") != -1) return 'NetPositive';
if (agt.indexOf("phoenix") != -1) return 'Phoenix';
if (agt.indexOf("firefox") != -1) return 'Firefox';
if (agt.indexOf("safari") != -1) return 'Safari';
if (agt.indexOf("skipstone") != -1) return 'SkipStone';
if (agt.indexOf("msie") != -1) return 'Internet Explorer';
if (agt.indexOf("netscape") != -1) return 'Netscape';
if (agt.indexOf("mozilla/5.0") != -1) return 'Mozilla';
if (agt.indexOf('\/') != -1) {
if (agt.substr(0,agt.indexOf('\/')) != 'mozilla') {
return navigator.userAgent.substr(0,agt.indexOf('\/'));
}else
 return 'Netscape';
}else if (agt.indexOf(' ') != -1)
return navigator.userAgent.substr(0,agt.indexOf(' '));
else 
  return navigator.userAgent;
}
// Global events (every key press) 
 
var browser = whichBrs();
if(browser == 'Internet Explorer'){
document.onkeydown = function() { return !shouldCancelBackspace(event); }
}else if(browser == 'Firefox'){
document.onkeypress = function(e) { return !shouldCancelBackspace(e); } 
}
</script>

Disable backspace key sample code

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