无法从For循环内部从For循环外部访问数据
无法从For循环内部从For循环外部访问数据
提问于 2019-12-11 15:39:41
我无法访问推送到for loop之外声明的变量的数组数据。
let tickets = [];
(async () => {
for (let chunk of chunks) {
try {
let ticketChunk = await someMethod(chunk)
tickets.push(...ticketChunk)
console.log("first log", tickets)
} catch (error) {
console.error(error)
}
}
})();
console.log("second log", tickets)上面的代码正确地显示了第一个日志上tickets变量中的数组，但是第二个日志显示为空。
回答 3
Stack Overflow用户
回答已采纳
发布于 2019-12-11 15:51:05
假设chunks和ticketChunk都是数组，并且允许并行调用someMethod()，下面是一种使用map()和flat()的更简单、更快的方法
Promise.all(
chunks.map(async chunk => {
try {
const ticketChunk = await someMethod(chunk);
// some other async functions...
return ticketChunk;
} catch (error) {
console.error(error);
return [];
}
})
).then(ticketChunks => {
const tickets = ticketChunks.flat();
console.log(tickets);
});如果chunks或ticketChunk不是数组，则可以使用发生器函数复制上述行为：
function* map(iterable, callback) {
for (const value of iterable) {
yield callback(value);
}
}
function isIterable(arg) {
return typeof Object(arg)[Symbol.iterator] === 'function';
}
function* flat(iterable, depth = 1) {
for (const value of iterable) {
// value !== iterable prevents recursion on unit length strings
if (depth > 0 && isIterable(value) && value !== iterable) {
yield* flat(value, depth - 1);
} else {
yield value;
}
}
}
Promise.all(
map(chunks, async chunk => {
try {
const ticketChunk = await someMethod(chunk);
// some other async functions...
return ticketChunk;
} catch (error) {
console.error(error);
return [];
}
})
).then(ticketChunks => {
const tickets = [...flat(ticketChunks)];
console.log(tickets);
});Stack Overflow用户
发布于 2019-12-11 15:48:51
因为“主”函数是异步的。
试着：
let tickets = [];
for (let chunk of chunks) {
try {
let ticketChunk = await someMethod(chunk)
tickets.push(...ticketChunk)
console.log("first log", tickets)
} catch (error) {
console.error(error)
}
}
console.log("second log", tickets);或
let tickets = [];
const someStuff = async() => {
for (let chunk of chunks) {
try {
let ticketChunk = await someMethod(chunk)
tickets.push(...ticketChunk)
console.log("first log", tickets)
} catch (error) {
console.error(error)
}
}
}
await someStuff();
console.log("second log", tickets);Stack Overflow用户
发布于 2019-12-11 15:48:03
在尝试处理加载在其中的数据之前，您需要等待必须执行的异步函数。看起来有点像这样：
let tickets = [];
(async () => {
for (let chunk of chunks) {
try {
let ticketChunk = await someMethod(chunk)
tickets.push(...ticketChunk)
console.log("first log", tickets)
} catch (error) {
console.error(error)
}
}
})().then(() => {
console.log("second log", tickets)
});页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/59289279
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