useSubscription()

function useSubscription(
  fetchShape: ReadShape,
  params: object | null,
): void;

function useSubscription<
  Params extends Readonly<object>,
  S extends Schema
>(
  fetchShape: ReadShape<S, Params>,
  params: Params | null,
): void;

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

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

Send null to params to unsubscribe.

Example

PriceResource.ts

import { Resource, FetchOptions } from 'rest-hooks';

export default class PriceResource extends Resource {
  readonly symbol: string | undefined = undefined;
  readonly price: string = '0.0';
  // ...

  pk() {
    return this.symbol;
  }
  static urlRoot = 'http://test.com/price/';

  /** Used as default options for every FetchShape */
  static getFetchOptions(): FetchOptions {
    return {
      pollFrequency: 5000, // every 5 seconds
    };
  }
}

MasterPrice.tsx

import { useResource, useSubscription } from 'rest-hooks';
import PriceResource from 'resources/PriceResource';

function MasterPrice({ symbol }: { symbol: string }) {
  const price = useResource(PriceResource.detailShape(), { symbol });
  useSubscription(PriceResource.detailShape(), { symbol });
  // ...
}

Only subscribe while element is visible

MasterPrice.tsx

import { useRef } from 'react';
import { useResource, useSubscription } from 'rest-hooks';
import PriceResource from 'resources/PriceResource';

function MasterPrice({ symbol }: { symbol: string }) {
  const price = useResource(PriceResource.detailShape(), { symbol });
  const ref = useRef();
  const onScreen = useOnScreen(ref);
  // null params means don't subscribe
  useSubscription(PriceResource.detailShape(), 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 FetchShapes to send

Resource provides these built-in:

• detailShape()
• listShape()

Be sure to extend these FetchShapes with a pollFrequency to set the polling-rate.