标题中提到的问题：console.log显示正确的值，但是当我返回它并通过在段落中添加一个段落（使用jQuery）将其与DOM一起显示时，它显示未定义...
console.log(dateTimeUTC(timeZoneStr));
// Shows the correct value I wanted
return dateTimeUTC(timeZoneStr);
// Shows undefined
所以我想做的是：使用带有简单输入文本和提交按钮的html表单，单击提交按钮时，它将使用jQuery将输入的文本保存在变量中：let variable = $('#cityName').val();（该值应为城市名称），因为当我获得城市名称值时，我要求openweathermap API向我发送json并以ms为单位给出时区的值，那么我需要将ms值转换为小时，因此例如，纽约，：时区：-14400（json.timezone / 60 / 60)，因此纽约的结果是UTC-4，那么我有一个脚本可以将我的UTC事物转换为实时日期，但是该脚本可以工作，所以我不需要向您解释...函数完成后，它会给我这样的结果：
2019年8月13日星期二05:53:39 GMT + 0200 不太适合演示，因此我做了一个函数，可以更好地转换它：
year = timeNow.getFullYear();
month = ('0'+(timeNow.getMonth()+1)).slice(-2);
day = ('0'+timeNow.getDate()).slice(-2);
hour = ('0'+timeNow.getHours()).slice(-2);
minute = ('0'+timeNow.getMinutes()).slice(-2);
second = ('0'+timeNow.getSeconds()).slice(-2);
showDateTimeValue = day + "/" + month + "/" + year + " - " + hour + ":" + minute + ":" + second;
return showDateTimeValue;
然后，此返回值转到我执行该函数的位置，因此在名为timeZone的函数中，在那里我已经使console.log工作，但返回时它显示未定义。
希望我能很好地解释您的想法，如果有人可以帮助我，您会明白我的意思。^ _ ^
编辑-完整代码：
Index.html代码：
<div class="form-group">
<label for="cityName">Displays the local date and time according to the name of the city</label>
<input name="cityName" type="text" id="cityName" placeholder="Enter a name of a city..." class="form-control">
</div>
<br>
<button type="submit" id="submit">Submit</button>
<p class="results"></p>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
<script src="./scripts/main.js"></script>
main.js代码：
$(function () {
$( "#submit" ).click(function() {
let city = $('#cityName').val();
cityName = city.split(' ').join('+');
if(cityName === "") {
$('.results').append("<p>Wrong location.</p>");
}
else {
$('.results').append("<p>The date and time of " + city + " : " + weatherRequest("http://api.openweathermap.org/data/2.5/weather?q=" + cityName + "&units=metric&appid=MyAPIkey") +'</p>');
}
});
})
功能代码：
/* Function variable */
const messageError = "You didn't enter a valid thing.";
let timeNow = new Date();
let utcOffset = timeNow.getTimezoneOffset();
timeNow.setMinutes(timeNow.getMinutes() + utcOffset);
// Function that gives the date and hour utc time
function dateTimeUTC(utc) {
if(typeof utc === 'string' && utc.length >= 1 && utc[0] === '-' || '0' || '+' || !isNaN(parseFloat(utc[0])))
{
if (utc[0] === '0' && utc.length === 1)
{
let enteredOffset = 0;
return showDateTime(enteredOffset);
}
else if (utc[0] === '+' || !isNaN(parseFloat(utc[0])))
{
if (utc.length === 2 && utc[0] === '+')
{
// Entered offset
let enteredOffset = parseFloat(utc[1])*60;
timeNow.setMinutes(timeNow.getMinutes() + enteredOffset);
return showDateTime(enteredOffset);
}
else if (utc.length === 3 && utc[0] === '+')
{
// Entered offset
let enteredOffset = parseFloat(utc[1] + utc[2])*60;
timeNow.setMinutes(timeNow.getMinutes() + enteredOffset);
return showDateTime(enteredOffset);
}
else if (utc.length === 1 && !isNaN(parseFloat(utc[0])))
{
// Entered offset
let enteredOffset = parseFloat(utc[0])*60;
timeNow.setMinutes(timeNow.getMinutes() + enteredOffset);
return showDateTime(enteredOffset);
}
else if (utc.length === 2 && !isNaN(parseFloat(utc[0])))
{
// Entered offset
let enteredOffset = parseFloat(utc[0] + utc[1])*60;
timeNow.setMinutes(timeNow.getMinutes() + enteredOffset);
return showDateTime(enteredOffset);
}
else
{
let enteredOffset = 0;
return showDateTime(enteredOffset);
}
}
else if (utc[0] === '-')
{
if (utc.length === 2 && utc[0] === '-')
{
// Entered offset
let enteredOffset = - parseFloat(utc[1])*60;
timeNow.setMinutes(timeNow.getMinutes() + enteredOffset);
return showDateTime(enteredOffset);
}
else if (utc.length === 3 && utc[0] === '-')
{
// Entered offset
let enteredOffset = - parseFloat(utc[1] + utc[2])*60;
timeNow.setMinutes(timeNow.getMinutes() + enteredOffset);
return showDateTime(enteredOffset);
}
else
{
let enteredOffset = 0;
return showDateTime(enteredOffset);
}
}
else
{
let enteredOffset = 0;
return showDateTime(enteredOffset);
}
}
else if (utc === '' || !utc || utc === undefined)
{
utc = false;
let enteredOffset = 0;
return showDateTime(enteredOffset);
}
else
{
let enteredOffset = 0;
return showDateTime(enteredOffset);
}
}
// Function that shows the date and time correctly (format : dd/mm/yyyy - 00:00:00)
function showDateTime(enteredOffset) {
year = timeNow.getFullYear();
month = ('0'+(timeNow.getMonth()+1)).slice(-2);
day = ('0'+timeNow.getDate()).slice(-2);
hour = ('0'+timeNow.getHours()).slice(-2);
minute = ('0'+timeNow.getMinutes()).slice(-2);
second = ('0'+timeNow.getSeconds()).slice(-2);
showDateTimeValue = day + "/" + month + "/" + year + " - " + hour + ":" + minute + ":" + second;
timeNow.setMinutes(timeNow.getMinutes() - enteredOffset)
return showDateTimeValue;
}
// Function which get the shift in seconds between the utc with the API
function timeZone(json) {
let timeZone = json.timezone / 60 / 60;
let timeZoneStr = timeZone.toString();
// console.log("La date et l'heure de " + cityName.split('+').join(' ') + " : " + dateTimeUTC(timeZoneStr));
console.log(dateTimeUTC(timeZoneStr)); // Shows the correct value I wanted
return dateTimeUTC(timeZoneStr); // Shows undefined
}
// Function that request the openweathermap.org API
function weatherRequest(url) {
// console.log(url);
try
{
$.getJSON(url, function(json) {
timeZone(json);
});
}
catch
{
console.log("Wrong location.");
}
}
答案 0 :(得分：0)
好的，有人可以帮助我找出错误的原因，所以这里是解决方案： 由于我们无法确定请求何时结束，因此您无法在getJSON之外返回值，因此您需要将想要的内容直接附加到getJSON东西中，所以这是main.js中的代码：
$( "#submit" ).click(function()
{
let city = $('#cityName').val();
let cityName = city.split(' ').join('+');
if(cityName === "")
{
$('.results').append("<p>Wrong location.</p>");
}
else
{
weatherRequest("http://api.openweathermap.org/data/2.5/weather?q=" + cityName + "&units=metric&appid=MyAPIkey");
}
});
仅需要更改功能weatherRequest：
function weatherRequest(url) {
// console.log(url);
try
{
$.getJSON(url, function callbackSuccess(json) {
let showDateTimeValue = timeZone(json);
let city = json.name;
$('.results').append("<p>The date and time of " + city + " : " + showDateTimeValue + '</p>');
});
}
catch
{
$('.results').append("<p>Wrong location.</p>");
}
}
希望您能理解，我不好解释，是的...