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Javascript Polling with Promises
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var Promise = require('bluebird'); | |
/** | |
* Periodically poll a signal function until either it returns true or a timeout is reached. | |
* | |
* @param signal function that returns true when the polled operation is complete | |
* @param interval time interval between polls in milliseconds | |
* @param timeout period of time before giving up on polling | |
* @returns true if the signal function returned true, false if the operation timed out | |
*/ | |
function poll(signal, interval, timeout) { | |
function pollRecursive() { | |
return signal() ? Promise.resolve(true) : Promise.delay(interval).then(pollRecursive); | |
} | |
return pollRecursive() | |
.cancellable() | |
.timeout(timeout) | |
.catch(Promise.TimeoutError, Promise.CancellationError, function () { | |
return false; | |
}); | |
} | |
/** | |
* Every 2 seconds, call a signal function that returns true 25% of the time. Timeout after 10 seconds. | |
*/ | |
poll(randomSignal, 2000, 10000).then(console.log); | |
function randomSignal() { | |
var r = Math.random() <= 0.25; | |
console.log(r ? "Complete" : "Not complete"); | |
return r; | |
} |
@jopek, I ran into the same issue! What is the preferred way of making a polling function with promises now?
module.exports.pollUntil = function(fn, delay){
var notCanceled = true;
function pollRecursive(){
return Promise.resolve().then(fn).then((boo)=>(
notCanceled && boo && new Promise((res)=>(setTimeout(res, delay)))
.then(pollRecursive)
));
}
var p = pollRecursive();
p.cancel = ()=>(
notCanceled = false
);
};
@formula1, thanks for this!
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.cancellable()
doesn't exist anymore. so the timeout does not have any breaking effect.how does one exit the polling after timeout?