所以我有這個函數(shù)，我希望程序等待它返回一個值而不是給出未定義的值。function savedNumberOfLessonInDay(dayID){ var xhttp = new XMLHttpRequest(); xhttp.onreadystatechange = function() { if (this.readyState == 4 && this.status == 200) { document.getElementById('demo4').innerHTML = this.responseText; //Returns the right number return this.responseText; } }; var PageToSendTo = "AJAX/countLessonInDay.php?"; var MyVariable = dayID; var VariablePlaceholder = "GETDayID="; var UrlToSend = PageToSendTo + VariablePlaceholder + MyVariable; xhttp.open("GET", UrlToSend, false); xhttp.send(); }<?phprequire '../notWebsite/dbh.php';session_start();$dayID = (int)$_GET['GETDayID'];$sqlCount = "SELECT COUNT(lessonID) FROM daylesson WHERE dayID = ?"; $stmt = mysqli_stmt_init($conn); if(!mysqli_stmt_prepare($stmt, $sqlCount)) { header("Location: ../GymnasieArbeteHemsida.php?error=countError"); exit(); } else { mysqli_stmt_bind_param($stmt, "i", $dayID);//Puts in variable in question mysqli_stmt_execute($stmt);//Executes the questionmysqli_stmt_bind_result($stmt, $result);//Binds the reuslt of the question to the variable $resultif(mysqli_stmt_fetch($stmt)){//If the result of the question can be recieved echo $result;//Send the result to the website} exit(); } mysqli_stmt_close($stmt); mysqli_close($conn); ?> document.getElementById('demo').innerHTML = 'test' + savedNumberOfLessonInDay(number);此代碼將 testundefined 返回給 demo，但將 16（這是我要的數(shù)字）返回給 demo4。如何讓它返回 test16 而不是 testundefined？
3 回答
慕萊塢森
TA貢獻1810條經(jīng)驗 獲得超4個贊
你不能打電話savedNumberOfLessonInDay(number)來獲取號碼。您正在嘗試使用 執(zhí)行此操作return this.responseText;，但在對服務器的請求完成之前不會觸發(fā)。
你可以使用 Promises 來解決這個問題。
function savedNumberOfLessonInDay(dayID){
return new Promise((resolve) => {
var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
document.getElementById('demo4').innerHTML = this.responseText; //Returns the right number
resolve(this.responseText);
}
};
var PageToSendTo = "AJAX/countLessonInDay.php?";
var MyVariable = dayID;
var VariablePlaceholder = "GETDayID=";
var UrlToSend = PageToSendTo + VariablePlaceholder + MyVariable;
xhttp.open("GET", UrlToSend, false);
xhttp.send();
});
}
并用await它來稱呼它：
document.getElementById('demo').innerHTML = 'test' + await savedNumberOfLessonInDay(number);
或者，如果由于某種原因您不能使用await：
savedNumberOfLessonInDay(number).then((response) => {
document.getElementById('demo').innerHTML = 'test' + response;
});
拉丁的傳說
TA貢獻1789條經(jīng)驗 獲得超8個贊
函數(shù) savedNumberOfLessonInDay() 不會等待 ajax 完成。所以需要在回調函數(shù)xhttp.onreadystatechange中設置demo的html。
在不改變你的實現(xiàn)太多的情況下，你可以簡單地修改你的代碼：
function savedNumberOfLessonInDay(dayID){
var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
document.getElementById('demo4').innerHTML = this.responseText; //Returns the right number
document.getElementById('demo').innerHTML = 'test' + this.responseText;
}
};
var PageToSendTo = "AJAX/countLessonInDay.php?";
var MyVariable = dayID;
var VariablePlaceholder = "GETDayID=";
var UrlToSend = PageToSendTo + VariablePlaceholder + MyVariable;
xhttp.open("GET", UrlToSend, false);
xhttp.send();
}
然后只需調用該函數(shù)而不是嘗試設置
savedNumberOfLessonInDay(number);
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