(function(){

     var doc=document,

         ua = navigator.userAgent.toLowerCase(),

         check = function(r){return r.test(ua);},

         isOpera = check(/opera/),

         isChrome = check(/chrome/),

         isWebKit = check(/webkit/),

         isSafari = !isChrome && check(/safari/),

         isSafari2 = isSafari && check(/applewebkit\/4/),

         isSafari3 = isSafari && check(/version\/3/),

         isSafari4 = isSafari && check(/version\/4/),

         isIE = !isOpera && check(/msie/),

         isIE7 = isIE && check(/msie 7/),

         isIE8 = isIE && check(/msie 8/),

         isIE9 = isIE && check(/msie 9/),

         isIE10 = isIE && check(/msie 10/),

         isIE11 = isIE && check(/msie 11/),

         isIE6 = isIE && !isIE7 && !isIE8 && !isIE9 && !isIE10 && !isIE11,

         isGecko = !isWebKit && check(/gecko/),

         isGecko2 = isGecko && check(/rv:1\.8/),

         isGecko3 = isGecko && check(/rv:1\.9/);

     function preventKey(e) {

         var ev = e || window.event,//获取event对象

         obj = ev.target || ev.srcElement,//获取事件源

         t = obj.type || obj.getAttribute('type'),readonly = obj.readOnly||obj.getAttribute('readonly'), code = ev.keyCode||ev.which||ev.charCode,charcode = String.fromCharCode(code).toLowerCase();//获取事件源控件类型,控件只读属性，键盘值

         if ( (code == 8 && t != "password" && t != "text" && t != "textarea")||(readonly&&(t == "password" || t == "text" || t == "textarea"))) {//除不只读输入框外禁止后退键

             return false;

         }

         if (((isOpera || isGecko)?ev.which==0:true)&&(code == 116 || code == 122|| code == 123 || (ev.shiftKey && code == 121))||(((isOpera || isGecko)?ev.which!=0:true)&&ev.ctrlKey && (charcode == 'a' || charcode == 's'))) {//屏蔽 F5,F11,F12,shift+F10,ctrl+a,ctrl+s

             if (isIE)

                 ev.keyCode = 0;

             ev.returnValue = false;

             return false;

         }

     };

     if (isOpera || isGecko)

         doc.onkeypress = preventKey;

     else if (isIE || isChrome || isSafari)

         doc.onkeydown = preventKey;

     if(isIE)document.onselectstart=function(){return false;};

     doc.oncontextmenu = function(){

         if(window.event){

             window.event.cancelBubble = true;

             window.event.returnValue=false;

         }

         return false;

     };

     try{window.history.forward(1);}catch(e){}

 })();