suspend-react

}>


)
}
`

#### API

`tsx
const suspend = , Fn extends (...keys: Keys) => Promise>(
fn: Fn | Promise,
keys?: Keys,
config?: Config
) => Await>
`

`tsx
// Function that returns a promise
const result = suspend((...keys) => anyPromise, keys, config)
// async function
const result = suspend(async (...keys) => { / ... / }, keys, config)
// Promise with keys
const result = suspend(anyPromise, keys, config)
// Promise itself is the key
const result = suspend(anyPromise)
`

suspend yields control back to React and the render-phase is aborted. It will resume once your promise resolves. For this to work you need to wrap it into a block, which requires you to set a fallback (can be null).

The dependencies (the 2nd argument) act as cache-keys, use as many as you want. If an entry is already in cache, calling suspend with the same keys will return it _immediately_ without breaking the render-phase. Cache access is similar to useMemo but across the component tree.

The 1st argument has to be a promise, or a function that returns a promise, or an asyn function. It receives the keys as arguments. suspend will return the resolved value, not a promise! This is guaranteed, you do not have to check for validity. Errors will bubble up to the nearest error-boundary.

#### Config

Both suspend and preload can _optionally_ receive a config object,

###### Keep-alive

The lifespan prop allows you to invalidate items over time, it defaults to 0 (keep-alive forever). Every read refreshes the timer to ensure that used entries stay valid.

`jsx
// Keep cached item alive for one minute without read
suspend(fn, keys, { lifespan: 60000 })
`

###### Equality function

The equal prop customizes per-key validation, it defaults to (a, b) => a === b (reference equality).

`jsx
import equal from 'fast-deep-equal'

// Validate keys deeply
suspend(fn, keys, { equal })
`

#### Preloading

`jsx
import { preload } from 'suspend-react'

async function fetchFromHN(id, version) {
const res = await fetch(https://hacker-news.firebaseio.com/${version}/item/${id}.json)
return res.json()
}

preload(fetchFromHN, [1000, 'v0'])
`

#### Cache busting

`jsx
import { clear } from 'suspend-react'

// Clear all cached entries
clear()
// Clear a specific entry
clear([1000, 'v0'])
`

#### Peeking into entries outside of suspense

`jsx
import { peek } from 'suspend-react'

// This will either return the value (without suspense!) or undefined
peek([1000, 'v0'])
`

#### Making cache-keys unique

Since suspend operates on a global cache (for now, see React 18), you might be wondering if keys could bleed, and yes they would. To establish cache-safety, create unique or semi-unique appendixes.

`diff
- suspend(fn, [1000, 'v0'])
+ suspend(fn, [1000, 'v0', 'functionName/fetch'])
`

If you publish a library that suspends, consider symbols.

`jsx
const fetchUUID = Symbol()

export function Foo() {
suspend(fn, [1000, 'v0', fetchUUID])
``

#### Typescript

Correct types will be inferred automatically.

#### React 18

Suspense, as is, has been a stable part of React since 16.6, but React will likely add some interesting caching and cache busting APIs that could allow you to define cache boundaries declaratively. Expect these to be work for suspend-react once they come out.

#### Demos

Fetching posts from hacker-news: codesandbox

Infinite list: codesandbox