屏蔽BcakSpace、F5 、CTRL+R 刷新键

var checkSpecialKey = function(e){    e=e||window.event;    var k = e.which||e.keyCode;    //屏蔽   BcakSpace   后退键    //屏蔽   F5   刷新键    //屏蔽 CTRL+R 刷新键    if(k == 8 || k == 116 || (e.ctrlKey && k == 82 ) ){        if(e.preventDefault){            e.preventDefault();        }else{            e.keyCode = 0;            e.returnValue=false;        }    }}if(document.addEventListener){    document.addEventListener("keydown",checkSpecialKey,false);}else{    document.attachEvent("onkeydown",checkSpecialKey);}