async-retry-ng


Retrying made simple, easy, and async.

Usage

``js
// Packages
const retry = require('async-retry-ng')
const fetch = require('node-fetch')

await retry(async bail => {
// if anything throws, we retry
const res = await fetch('https://google.com')

if (403 === res.status) {
// don't retry upon 403
bail(new Error('Unauthorized'))
return
}

const data = await res.text()
return data.substr(0, 500)
}, {
retries: 5
})
`

$3

`js
retry(retrier : Function, opts : Object) => Promise
`

- The supplied function can be async or not. In other words, it can be a function that returns a Promise or a value.
- The supplied function receives two parameters
1. A Function you can invoke to abort the retrying (bail)
2. A Number identifying the attempt. The absolute first attempt (before any retries) is 1.
- The opts
* retries: The maximum amount of times to retry the operation. Default is 10.
* factor: The exponential factor to use. Default is 2.
* minTimeout: The number of milliseconds before starting the first retry. Default is 1000.
* maxTimeout: The maximum number of milliseconds between two retries. Default is Infinity.
* randomize: Randomizes the timeouts by multiplying with a factor between 1 to 2. Default is true.
* onRetry: an optional Function that is invoked after a new retry is performed. It's passed the Error that triggered it as a parameter.

All time values are in milliseconds.

$3

The formula used to calculate the individual timeouts is:

`
Math.min(random minTimeout Math.pow(factor, attempt), maxTimeout)
`

Have a look at [this article][article] for a better explanation of approach.

If you want to tune your factor / times settings to attempt the last retry
after a certain amount of time, you can use wolfram alpha. For example in order
to tune for 10 attempts in 5 minutes, you can use this equation:

!screenshot

Explaining the various values from left to right:

* k = 0 ... 9: The retries value (10)
* 1000: The minTimeout value in ms (1000)
* x^k: No need to change this, x will be your resulting factor
5 60 * 1000`: The desired total amount of time for retrying in ms (5 minutes)

To make this a little easier for you, use wolfram alpha to do the calculations:

x^k%2C+{k%2C+0%2C+9}%5D+%3D+5++60+*+1000>

[article]: http://dthain.blogspot.com/2009/02/exponential-backoff-in-distributed.html