//提取歌詞function getLyric(url){var request=null;var lyricLines;  if(window.XMLHttpRequest){     request=new XMLHttpRequest() }else{     request=new ActiveXObject("Microsoft.XMLHTTP"); } request.open("GET",url,true); request.send(); request.onreadystatechange=function(){    if(request.readyState===4){        if(request.status===200){             lyricLines=request.responseText.split("\n");            return lyricLines;         }else{             alert("出現錯誤："+request.status);         }     } };//返回函數不代表返回函數的返回值，因為返回的函數并沒有被執行//應該返回request.onreadystatechange函數所返回的值return ?;}怎樣才能返回lyricLines呢