[英]Fetch array data from inside function scope
我目前正在嘗試使用已在函數作用域內填充的數組。 我的主要問題是,每當我嘗試將數組作為信息發送時,系統就會告訴我它為空。
野兔是我的嵌套函數:
exports.getUserDetails = async function(req ,res ,next){
try{
Stats.find({map:"France"}).sort({lapTime:1}).limit(3).then(response =>{
var resultArray=[]; // <----Here is where I've innitialised my array
for(var item = 0; item < response.length; item++){
const singleDriverId = response[item].driver;
const playedMap = response[item].map; // single Map etry from the stats Object
const timedLap = response[item].lapTime; //single lapTime entry from the stats Object
User.find({"_id" : singleDriverId}, function(err, result){
if (err) throw err;
for (var i = 0; i< result.length; i++){
//setting up the Object to populate the Array.
var finalResult = {
"driver": result[i].firstName + " " + result[i].lastName,
"map": playedMap,
"laptime": timedLap
}
//<------populating the Array
resultArray.push(finalResult);
}
});
}
console.log(resultArray) // prints an empty Array []
res.status(200).json({status: 200, data: resultArray, message: "Successfully got the user details."});
})
}catch(error){
console.log(error);
res.status(400);
}
}
我認為以某種方式resultArray.push(finalResult);
我有機會打印之前的“空”字嗎?
有人對為什么會發生這種情況有什么建議,我該如何解決?
我正在嘗試從
resultArray.push(finalResult)
接收單個數組
您問題的通用示例(javascript的異步特性)
function getData(cb) { setTimeout(() => cb(Date.now()), Math.random() * 1000); } const result = []; for (var i = 0; i < 10; i++) { getData((data) => { result.push(data); }); } console.log(result); // empty :O
通用的解決方案(運行done
,當一切都完成):
function getData(cb) { setTimeout(() => cb(Date.now()), Math.random() * 1000); } const result = []; const count = 10; for (var i = 0; i < count; i++) { getData((data) => { result.push(data); done(); }); } var called = 0; function done() { called++; if (called === count) { console.log(result); // desired result \\O/ } }
當然,現在有了promise和async / await,一切都變得更加簡單(使用async / await,它看起來幾乎就像是一個同步代碼)。 有多篇文章以及如何使用它們的教程。
對於您的代碼,它應該是這樣的(請注意,當您執行網絡請求時,響應的順序可能與發送請求的順序不同,因此resultArray
的項可能與響應中的項不完全對應):
exports.getUserDetails = async function(req ,res ,next){
try{
Stats.find({map:"France"}).sort({lapTime:1}).limit(3).then(response =>{
var resultArray=[]; // <----Here is where I've innitialised my array
for(var item = 0; item < response.length; item++){
const singleDriverId = response[item].driver;
const playedMap = response[item].map; // single Map etry from the stats Object
const timedLap = response[item].lapTime; //single lapTime entry from the stats Object
User.find({"_id" : singleDriverId}, function(err, result){
if (err) throw err;
for (var i = 0; i< result.length; i++){
//setting up the Object to populate the Array.
var finalResult = {
"driver": result[i].firstName + " " + result[i].lastName,
"map": playedMap,
"laptime": timedLap
}
//<------populating the Array
resultArray.push(finalResult);
done(); // function is run whenever data is pushed
}
});
}
var count = 0;
function done() {
count++;
if (count === response.length) { // this code block is run only when all items are pushed into the resultArray
console.log(resultArray)
}
}
res.status(200).json({status: 200, data: resultArray, message: "Successfully got the user details."});
})
}catch(error){
console.log(error);
res.status(400);
}
}
可能User.find
也支持promise,因此使用Promise.all
方式更簡單,可讀性更好。
只需使用if語句,它將起作用
if(resultArray){console.log(resultArray)//打印一個空Array [] res.status(200).json({status:200,data:resultArray,消息:“已成功獲取用戶詳細信息。”}); }
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