监听回车事件记录

document.onkeydown=keyDownSearch;
     function keyDownSearch(e) {   
        // 兼容FF和IE和Opera   
        var theEvent = e || window.event;   
        var code = theEvent.keyCode || theEvent.which || theEvent.charCode;   
        if (code == 13) {   
            alert(‘回车‘);//具体处理函数   
            return false;   
        }   
        return true;   
    }

 function getKey() 
{ 
    if(event.keyCode==13){ 
     alert("回车 ");
    }     
}

<input type="text" name="username" id="username" onkeypress="getKey();"></input>