Promises: Repeat operation until it succeeds?

javascript promise q
Jay Bienvenu picture Jay Bienvenu · Nov 2, 2014 · Viewed 11.7k times · Source

I want to perform an operation repeatedly, with an increasing timeout between each operation, until it succeeds or a certain amount of time elapses. How do I structure this with promises in Q?

Answer

Benjamin Gruenbaum picture Benjamin Gruenbaum · Nov 2, 2014

All the answers here are really complicated in my opinion. Kos has the right idea but you can shorten the code by writing more idiomatic promise code:

function retry(operation, delay) {
    return operation().catch(function(reason) {
        return Q.delay(delay).then(retry.bind(null, operation, delay * 2));
    });
}

And with comments:

function retry(operation, delay) {
    return operation(). // run the operation
        catch(function(reason) { // if it fails
            return Q.delay(delay). // delay 
               // retry with more time
               then(retry.bind(null, operation, delay * 2)); 
        });
}

If you want to time it out after a certain time (let's say 10 seconds , you can simply do:

var promise = retry(operation, 1000).timeout(10000);

That functionality is built right into Q, no need to reinvent it :)

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