Retrying made simple, easy and async
npm install async-retry-ng
Retrying made simple, easy, and async.
``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
})
`
`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.Function
- The supplied function receives two parameters
1. A you can invoke to abort the retrying (bail)Number
2. A identifying the attempt. The absolute first attempt (before any retries) is 1.opts
- The 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.
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 retry10
after a certain amount of time, you can use wolfram alpha. For example in order
to tune for attempts in 5 minutes, you can use this equation:
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 factor5 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:
[article]: http://dthain.blogspot.com/2009/02/exponential-backoff-in-distributed.html