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useSubscription()

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

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.

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.

Example​

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 });
  // ...
}
tip

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

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.

Useful Endpoints to send​

Resource provides these built-in:

  • get
  • getList

Feel free to add your own RestEndpoint as well.