# Installation
### Prerequisite: [install Wretch](https://github.com/elbywan/wretch#installation)
## Npm
```sh
npm i wretch-middlewares
```
## Cdn
```html
```
# Middlewares
| [Dedupe](#dedupe) | [Retry](#retry) | [Throttling cache](#throttling-cache) | [Delay](#delay) |
|-----|-----|-----|-----|
## Dedupe
**Prevents having multiple identical requests on the fly at the same time.**
#### Options
- *skip* : `(url, opts) => boolean`
If skip returns true, then the dedupe check is skipped.
- *key* : `(url, opts) => string`
Returns a key that is used to identify the request.
- *resolver* : `(response: Response) => Response`
This function is called when resolving the fetch response from duplicate calls.
By default it clones the response to allow reading the body from multiple sources.
#### Usage
```js
import wretch from 'wretch'
import { dedupe } from 'wretch-middlewares'
wretch().middlewares([
dedupe({
/* Options - defaults below */
skip: (url, opts) => opts.skipDedupe || opts.method !== 'GET',
key: (url, opts) => opts.method + '@' + url,
resolver: response => response.clone()
})
])./* ... */
```
## Retry
**Retries a request multiple times in case of an error (or until a custom condition is true).**
#### Options
- *delayTimer* : `milliseconds`
The timer between each attempt.
- *delayRamp* : `(delay, nbOfAttempts) => milliseconds`
The custom function that is used to calculate the actual delay based on the the timer & the number of attemps.
- *maxAttempts* : `number`
The maximum number of retries before resolving the promise with the last error. Specifying 0 means infinite retries.
- *until* : `(fetchResponse, error) => boolean | Promise`
The request will be retried until that condition is satisfied.
- *onRetry* : `({ response, error, url, options }) => { url?, options? } || Promise<{url?, options?}>`
Callback that will get executed before retrying the request. If this function returns an object having url and/or options properties, they will override existing values in the retried request. If it returns a Promise, it will be awaited before retrying the request.
- *retryOnNetworkError* : `boolean`
If true, will retry the request if a network error was thrown. Will also provide an 'error' argument to the `onRetry` and `until` methods.
- *resolver* : `(response: Response) => Response`
This function is called when resolving the fetch response from duplicate calls.
By default it clones the response to allow reading the body from multiple sources.
#### Usage
```js
import wretch from 'wretch'
import { retry } from 'wretch-middlewares'
wretch().middlewares([
retry({
/* Options - defaults below */
delayTimer: 500,
delayRamp: (delay, nbOfAttempts) => delay * nbOfAttempts,
maxAttempts: 10,
until: (response, error) => response && response.ok,
onRetry: null,
retryOnNetworkError: false,
resolver: response => response.clone()
})
])./* ... */
// You can also return a Promise, which is useful if you want to inspect the body:
wretch().middlewares([
retry({
until: response =>
response.json().then(body =>
body.field === 'something'
)
})
])
```
## Throttling cache
**A throttling cache which stores and serves server responses for a certain amount of time.**
#### Options
- *throttle* : `milliseconds`
The response will be stored for this amount of time before being deleted from the cache.
- *skip* : `(url, opts) => boolean`
If skip returns true, then the dedupe check is skipped.
- *key* : `(url, opts) => string`
Returns a key that is used to identify the request.
- *clear* `(url, opts) => boolean`
Clears the cache if true.
- *invalidate* `(url, opts) => string | RegExp | Array | null`
Removes url(s) matching the string or RegExp from the cache. Can use an array to invalidate multiple values.
- *condition* `response => boolean`
If false then the response will not be added to the cache.
- *flagResponseOnCacheHit* `string`
If set, a Response returned from the cache whill be flagged with a property name equal to this option.
#### Usage
```js
import wretch from 'wretch'
import { throttlingCache } from 'wretch-middlewares'
wretch().middlewares([
throttlingCache({
/* Options - defaults below */
throttle: 1000,
skip: (url, opts) => opts.skipCache || opts.method !== 'GET',
key: (url, opts) => opts.method + '@' + url,
clear: (url, opts) => false,
invalidate: (url, opts) => null,
condition: response => response.ok,
flagResponseOnCacheHit: '__cached'
})
])./* ... */
```
## Delay
**Delays the request by a specific amount of time.**
#### Options
- *time* : `milliseconds`
The request will be delayed by that amount of time.
#### Usage
```js
import wretch from 'wretch'
import { delay } from 'wretch-middlewares'
wretch().middlewares([
delay(1000)
])./* ... */
```
