问题
I have this promise:
function getAPI(token)
{
return new Promise((resolve, reject) => {
console.log("Request API");
GM_xmlhttpRequest({
method: "GET",
url: "URL"+token,
onload: function(response) {
console.log(response.responseText);
if( response.responseText == "NOT_ANSWER" || response.responseText.indexOf("ERRO") > -1 ){
console.log(response.responseText + " - Calling Myself in 5 Seconds");
setTimeout(function(){
getAPI(token);
},5000);
}
else{
console.log('Call API - Giving Result');
resolve(response.responseText.split("_")[1]);
}
}
});
});
}
I call it inside of itself when the answer is not what I want, cannot be less than 5 seconds though.
Then I do this in the main function:
setTimeout( function(){
getAPI(token).then((key) => {
console.log(key);
doSomethingWithKey;
setTimeout( function(){
loop();
},1000);
}).catch(() => {
console.log('Error na api - reload page!');
location.reload();
});
},25000);
But I noticed that when getAPI calls itself cause answer is not what i want, the '.then' in the main function never executes and my code hangs there. How can I fix it? I don't understand much of promises but I can't see why it hangs ...
回答1:
I call it inside of itself when the answer is not what i want,
and then you don't call resolve
of the promise which you had returned from the top getAPI
call, so the promise never settles and your then
callback never gets any result.
You should promisify your asynchronous functions GM_xmlhttpRequest
and setTimeout
on the lowest level, and then only chain your promises. By return
ing the result of the recursive call from a then
callback, the resulting promise will resolve with the same result:
function xhrAsync(url) {
return new Promise((resolve, reject) => {
GM_xmlhttpRequest({
method: "GET",
url: url,
onload: resolve
});
});
}
function delayAsync(time) {
return new Promise(resolve => {
setTimeout(resolve, time);
});
}
function getAPI(token) {
console.log("Request API");
return xhrAsync("URL"+token).then(response => {
// ^^^^^^ ^^^^
console.log(response.responseText);
if (response.responseText == "NOT_ANSWER" || response.responseText.includes("ERRO")) {
console.log(response.responseText + " - Calling Myself in 5 Seconds");
return delayAsync(5000).then(() => {
// ^^^^^^ ^^^^
return getAPI(token);
// ^^^^^^
});
} else {
console.log('Call API - Giving Result');
return response.responseText.split("_")[1];
}
});
}
回答2:
You're creating multiple promises, because each call to getAPI
creates and returns a new promise.
getAPI
shouldn't call itself (or if it does, it should pass the new promise into resolve
); instead, just retry the part within it you need to retry, something along these lines:
function getAPI(token) {
return new Promise((resolve, reject) => {
// Function to do the request
function doRequest() {
console.log("Request API");
GM_xmlhttpRequest({
method: "GET",
url: "URL" + token,
onload: function(response) {
console.log(response.responseText);
if (response.responseText == "NOT_ANSWER" || response.responseText.indexOf("ERRO") > -1) {
// Not what we wanted, retry
console.log(response.responseText + " - Calling Myself in 5 Seconds");
setTimeout(doRequest, 5000);
}
else {
console.log('Call API - Giving Result');
resolve(response.responseText.split("_")[1]);
}
}
});
}
doRequest();
});
}
Side note: Your code using getAPI
is checking for promise rejection, but nothing in getAPI
ever rejects the promise.
来源:https://stackoverflow.com/questions/47002027/promise-not-returning-value-of-request