general solution to retry a promise in javascript

Question

I try to give out a general solution for retrying a promise. Below is my way and comes an error of \"Uncaught (in promise)\".

How can I fix this problem?

Answer 1

The reason for what you asked about is that you're missing a call to resolve in your catch:

.catch(err => {
    if (tries > 0) {
        console.log(`tries with ${tries}`);
        resolve(tryAtMost(--tries, promise)); // <=== ****
    }
    else {
        reject(err)
    }
})

...and so you're creating a promise that is never handled by anything, and so if it rejects, you'll get an unhandled rejection.

---

But, tryAtMost has a problem: It cannot work with the information you've given it, because it doesn't know what to try. You need to pass it an executor, not a promise, because it's the work of the executor that you need to retry. This also makes the function a lot simpler:

function tryAtMost(tries, executor) {
    --tries;
    return new Promise(executor)
        .catch(err => tries > 0 ? tryAtMost(tries, executor) : Promise.reject(err));
}

Use:

tryAtMost(4, (resolve, reject) => {
    // The thing to (re)try
});

Example:

function tryAtMost(tries, executor) {
  console.log(`trying, tries = ${tries}`);
  --tries;
  return new Promise(executor)
    .catch(err => tries > 0 ? tryAtMost(tries, executor) : Promise.reject(err));
}

tryAtMost(4, (resolve, reject) => {
  const val = Math.random();
  if (val < 0.3) {
    resolve(val);
  } else {
    reject(val);
  }
})
.then(result => console.log(result))
.catch(err => console.error(err));