keys = new Array();
keys["f112"] = 'f1';
keys["f113"] = 'f2';
keys["f114"] = 'f3';
keys["f115"] = 'f4';
keys["f116"] = 'f5';
keys["f117"] = 'f6';
keys["f118"] = 'f7';
keys["f119"] = 'f8';
keys["f120"] = 'f9';
keys["f121"] = 'f10';
keys["f122"] = 'f11';
keys["f123"] = 'f12';

saveCode=""
function myFunc(code) {
  //alert('testing '+code)
}

document.onkeydown = function(){
 // Capture and remap F-key
  if(window.event && keys["f"+window.event.keyCode])  {
    saveCode=window.event.keyCode;
    window.event.keyCode = 505;
  }
  if(window.event && window.event.keyCode == 505) {
    // New action for keycode
    myFunc(saveCode)
    return false; // Must return false or the browser will execute old code
  }
  if (window.event) {
	 //Disable Ctrl + N
	 if (window.event.ctrlKey && window.event.keyCode == 78) {
		 myFunc(saveCode)
    	 return false;
	 }
  }
}