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Version: 7.3

useSubscription()

Great for keeping resources up-to-date with frequent changes.

When using the default polling subscriptions, frequency must be set in Endpoint, otherwise will have no effect.

tip

useLive() is a terser way to use in combination with useSuspense(),

Usage

api/Price.ts
import { Resource, Entity } from '@rest-hooks/rest';

export class Price extends Entity {
readonly symbol: string | undefined = undefined;
readonly price: string = '0.0';
// ...

pk() {
return this.symbol;
}
}

export const getPrice = new RestEndpont({
urlPrefix: 'http://test.com',
path: '/price/:symbol',
schema: Price,
pollFrequency: 5000,
});
MasterPrice.tsx
import { useSuspense, useSubscription } from '@rest-hooks/react';
import { getPrice } from 'api/Price';

function MasterPrice({ symbol }: { symbol: string }) {
const price = useSuspense(getPrice, { symbol });
useSubscription(getPrice, { symbol });
// ...
}

Behavior

Conditional Dependencies

Use null as the second argument on any rest hooks to indicate "do nothing."

// todo could be undefined if id is undefined
const todo = useSubscription(TodoResource.get, id ? { id } : null);
React Native

When using React Navigation, useSubscription() will sub/unsub with focus/unfocus respectively.

Examples

Only subscribe while element is visible

MasterPrice.tsx
import { useRef } from 'react';
import { useSuspense, useSubscription } from '@rest-hooks/react';
import { getPrice } from 'api/Price';

function MasterPrice({ symbol }: { symbol: string }) {
const price = useSuspense(getPrice, { symbol });
const ref = useRef();
const onScreen = useOnScreen(ref);
// null params means don't subscribe
useSubscription(getPrice, onScreen ? null : { symbol });

return (
<div ref={ref}>{price.value.toLocaleString('en', { currency: 'USD' })}</div>
);
}

Using the last argument active we control whether the subscription is active or not based on whether the element rendered is visible on screen.

useOnScreen() uses IntersectionObserver, which is very performant. useRef allows us to access the DOM.

Types

function useSubscription(
endpoint: ReadEndpoint,
...args: Parameters<typeof endpoint> | [null]
): void;