轮询直到得到特定的结果？
我目前正在尝试使用此链接https://davidwalsh.name/javascript-polling (以及许多其他链接)将轮询添加到我的应用程序中。
我可以访问以下已经实现的api：
client.get('url')
// returns Promise with result of getting result from url
// for the application I am working on,
// the URL returns json that looks like the following
// {status: DONE or IN PROGRESS, other values...}
// when status is DONE other values are what I will use in the application
client.post('url', {data: passAnyDataHere})
// sends a post request with result of sending data to url
// starts the specific job我遇到的一个问题是，当我尝试修改我链接到上面的JavaScript轮询代码时，当我发现状态是完成时，我无法将结果返回到Promise之外。有人能给我一些如何做到这一点的提示吗？(轮询直到我找到一个特定值，然后返回该值供以后使用)
让我给你举个例子
export default function someFunction() {
let a = client.get('/status');
a.then( dataResult =>
{
if (dataResult.status == "DONE") {
//** want to get other values in dataResult here
// and store it somewhere else for use later
}
});
// ***want to work with results here.
// need some way to get the status of what happened inside the .then(..) part
// eventually have to return success or failure and results to the frontend
// (this part is already done)
}代码的基础是https://github.com/erikras/react-redux-universal-hot-example#server-side-data-fetching (使用React.js/node.js/Redux/等)
感谢任何提示/建议/帮助。谢谢!
另外，我正在开发的应用程序不使用JQuery。
回答 8
Stack Overflow用户
发布于 2020-11-03 06:23:05
这是一个基于post polling with async/await的更具可扩展性的解决方案
只需添加以下实用程序方法：
const poll = async function (fn, fnCondition, ms) {
let result = await fn();
while (fnCondition(result)) {
await wait(ms);
result = await fn();
}
return result;
};
const wait = function (ms = 1000) {
return new Promise(resolve => {
setTimeout(resolve, ms);
});
};然后你可以这样叫它：
let fetchReport = () => axios.get(reportUrl);
let validate = result => !result.data.summary;
let response = await poll(fetchReport, validate, 3000);Stack Overflow用户
发布于 2017-09-14 07:36:23
Node.js的最新版本支持异步/等待。
下面是一个使用它的例子。
async / await的一个主要优点是，它很容易理解代码，并理解其逻辑。例如，如果你想扩展它，拥有一个最大的try's特性，这将是微不足道的。(提示)这只是一个for循环:)
let count = 0;
var client = {
get: function () {
return new Promise(function (resolve, reject) {
count ++;
setTimeout(function () {
if (count > 4) resolve({status:'DONE',otherStuff:'Other Stuff'});
else resolve({status: `count: ${count}`});
}, 1000);
});
}
}
async function someFunction() {
while (true) {
let dataResult = await client.get('/status');
console.log(dataResult.status);
if (dataResult.status == "DONE") {
return dataResult;
}
}
}
(async () => { let r = await someFunction(); console.log(r); })();
Stack Overflow用户
发布于 2017-09-14 07:54:46
下面是一个使用promises和polls直到您获得所需结果的函数的示例。我还对它进行了参数化，以便您可以传入轮询间隔和超时值：
// create a promise that resolves after a short delay
function delay(t) {
return new Promise(function(resolve) {
setTimeout(resolve, t);
});
}
// interval is how often to poll
// timeout is how long to poll waiting for a result (0 means try forever)
// url is the URL to request
function pollUntilDone(url, interval, timeout) {
let start = Date.now();
function run() {
return client.get(url).then(function(dataResult) {
if (dataResult.status === "DONE") {
// we know we're done here, return from here whatever you
// want the final resolved value of the promise to be
return dataResult;
} else {
if (timeout !== 0 && Date.now() - start > timeout) {
throw new Error("timeout error on pollUntilDone");
} else {
// run again with a short delay
return delay(interval).then(run);
}
}
});
}
return run();
}
// sample usage
// polls every 500ms for up to 30 seconds
pollUntilDone(someUrl, 500, 30 * 1000).then(function(result) {
// have final result here
}).catch(function(err) {
// handle error here
});这里的关键是链接您的承诺，这样每次您再次调用run()时，您都会返回它的值，以便它链接到先前的承诺。然后，当您最终返回一个值或抛出异常时，原始promise将获得该值或错误作为已解决的值或被拒绝的原因。
请注意，我添加了一个超时，因为您真的永远不想永远轮询，特别是在某些不可预见和重复出现的错误可能不会拒绝promise，但不会得到您想要的结果的情况下。
https://stackoverflow.com/questions/46208031
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