Promise Retry Design Patterns

by

Something a bit different …

Async retries can be achieved by building a .catch() chain, as opposed to the more usual .then() chain.

This approach is :

  • only possible with a specified maximum number of attempts. (The chain must be of finite length),
  • only advisable with a low maximum. (Promise chains consume memory roughly proportional to their length).

Otherwise, use a recursive solution.

First, a utility function to be used as a .catch() callback.

var t = 500;

function rejectDelay(reason) {
    return new Promise(function(resolve, reject) {
        setTimeout(reject.bind(null, reason), t); 
    });
}

Now you can build .catch chains very concisely :

1. Retry until the promise resolves, with delay

var max = 5;
var p = Promise.reject();

for(var i=0; i<max; i++) {
    p = p.catch(attempt).catch(rejectDelay);
}
p = p.then(processResult).catch(errorHandler);

DEMO: https://jsfiddle.net/duL0qjqe/

2. Retry until result meets some condition, without delay

var max = 5;
var p = Promise.reject();

for(var i=0; i<max; i++) {
    p = p.catch(attempt).then(test);
}
p = p.then(processResult).catch(errorHandler);

DEMO: https://jsfiddle.net/duL0qjqe/1/

3. Retry until result meets some condition, with delay

Having got your mind round (1) and (2), a combined test+delay is equally trivial.

var max = 5;
var p = Promise.reject();

for(var i=0; i<max; i++) {
    p = p.catch(attempt).then(test).catch(rejectDelay);
    // Don't be tempted to simplify this to `p.catch(attempt).then(test, rejectDelay)`. Test failures would not be caught.
}
p = p.then(processResult).catch(errorHandler);

test() can be synchronous or asynchronous.

It would also be trivial to add further tests. Simply sandwich a chain of thens between the two catches.

p = p.catch(attempt).then(test1).then(test2).then(test3).catch(rejectDelay);

DEMO: https://jsfiddle.net/duL0qjqe/3/

All versions are designed for attempt to be a promise-returning async function. It could also conceivably return a value, in which case the chain would follow its success path to the next/terminal .then().

More Related Contents:

  1. Removing nested promises
  2. Chained promises not passing on rejection
  3. Why is my asynchronous function returning Promise { } instead of a value?
  4. Issue in returning data retrieved from DB queries called in the loop
  5. Is “.then(function(a){ return a; })” a no-op for promises?
  6. Is Node.js native Promise.all processing in parallel or sequentially?
  7. Using async/await with a forEach loop
  8. Object method with ES6 / Bluebird promises
  9. Node JS Promise.all and forEach
  10. Limit concurrency of promise being run
  11. Understanding promises in Node.js
  12. Why is ‘this’ undefined inside class method when using promises? [duplicate]
  13. NodeJS Timeout a Promise if failed to complete in time
  14. Can’t throw error from within an async promise executor function
  15. for await of VS Promise.all
  16. How can I chain these functions together with promises?
  17. Getting a UnhandledPromiseRejectionWarning when testing using mocha/chai
  18. How can i return status inside the promise?
  19. Node exits without error and doesn’t await promise (Event callback)
  20. Nodejs express and promises not doing what I expect
  21. How do I handle errors with promises?
  22. Placement of catch BEFORE and AFTER then
  23. Why is `.catch(err => console.error(err))` discouraged?
  24. How to do promise.all for array of array of promises?
  25. What happens if i reject / resolve multiple times in Kriskowal’s q?
  26. Using mongoose promises with async/await
  27. Wait promise inside for loop
  28. Limit concurrency of pending promises
  29. javascript promise not passing all arguments (using Q)
  30. Node.js: When to use Promises vs Callbacks

Leave a Comment