Use reactive var hook

[jpvajda]

This PR attempts to better document the useReactivevVar hook introduced in #6867

[jpvajda]

👋 @alessbell @MrDoomBringer @hwillson @benjamn

Here's an attempt to document this feature! Could someone provide a quick review?

[hwillson]

Thanks @jpvajda! See my comments inline, but a few additional things:

1. I think we should move this new content down further on the page. The useReactiveVar hook is a nice feature, but it is additive to the reactive variable functionality of the Apollo Client core. For this reason, I think we should introduce people to reactive variables as a core library concept first, then introduce them to the hook. I think your content would fit well merged into the Reacting part of this page, replacing the With the useReactiveVar hook ... paragraph.

2. I think we should also document useReactiveVar alongside our other hooks, in the API section of the docs: https://www.apollographql.com/docs/react/api/react/hooks

Thanks again!

[jpvajda]

@hwillson I added to the API hooks docs, though you may want to review the function signature I pulled thatdefinition out of this change in the PR

[hwillson]

Awesome @jpvajda - just one more small thing then I think we're 👍. Thanks!

[alessbell]

Left a couple of stylistic nits that I'll let Stephen confirm/reject when he's back online, but overall found this very clear and easy to follow 😄

[jpvajda]

This is failing a single test in CI, but passes on my local branch.

Summary of all failing tests
 FAIL  link/batch/__tests__/batchLink.ts
  ● BatchLink › correctly follows batch interval

    expect(received).toBe(expected) // Object.is equality

    Expected: 2
    Received: 1

      622 |       // The batch shouldn't be fired yet, so we can add one more request.
      623 |       const sub3 = batcher.enqueueRequest({operation: operation3}).subscribe(() => reject('next should never be called'));
    > 624 |       expect(batcher["batchesByKey"].get('')!.size).toBe(2);
          |                                                     ^
      625 |
      626 |       sub3.unsubscribe();
      627 |       expect(batcher["batchesByKey"].get('')!.size).toBe(1);

      at link/batch/__tests__/batchLink.ts:624:53
      at Timeout.task [as _onTimeout] (../node_modules/jsdom/lib/jsdom/browser/Window.js:514:19)


Test Suites: 1 failed, 115 passed, 116 total
Tests:       1 failed, 15 skipped, 1769 passed, 1785 total
Snapshots:   135 passed, 135 total
Time:        83.38 s
Ran all test suites.

[jpvajda]

re running the test in Circle CI got it to pass. 🤷