JQuery实现防止退格键返回的方法

//浏览器中Backspace不可用 
$(document).keydown(function(e){  
       var keyEvent;  
       if(e.keyCode==8){  
           var d=e.srcElement||e.target;  
            if(d.tagName.toUpperCase()=='INPUT'||d.tagName.toUpperCase()=='TEXTAREA'){  
                keyEvent=d.readOnly||d.disabled;  
            }else{  
                keyEvent=true;  
            }  
        }else{  
            keyEvent=false;  
        }  
        if(keyEvent){  
            e.preventDefault();  
        }  
});  
 
//只防止input和textarea 浏览器中Backspace仍可用 
$(document).keydown(function(e){  
var keyEvent;  
if(e.keyCode==8){  
var d=e.srcElement||e.target;  
            if(d.tagName.toUpperCase()=='INPUT'||d.tagName.toUpperCase()=='TEXTAREA'){  
                keyEvent=d.readOnly||d.disabled;  
            } 
} else{ 
            keyEvent=false; 
} 
if(keyEvent){  
            e.preventDefault();  
        }  
});