Implement useReactiveVar hook for consuming reactive variables in React components. #6867
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Just to add - we'll want to get some docs for this in place as well. |
18 tasks
glasser
requested changes
Aug 20, 2020
glasser
reviewed
Aug 20, 2020
A common pitfall when using forEach to iterate over a set of callback functions, thankfully caught by the tests I wrote.
This restores the cache broadcast behavior prior to #6867, since @glasser persuaded me it could be risky to handle caches the same way we handle onNextChange listener functions: #6867 (comment) Unification is nice, but avoiding unnecessary breaking changes is nicer.
benjamn
commented
Aug 20, 2020
| return ( | ||
| <div class="add-to-cart-button"> | ||
| <Button onClick={() => cartItemsVar([...cartItems, productId])}> | ||
| <Button onClick={() => cartItemsVar([...cartItemsVar(), productId])}> |
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This was risky because the button could be clicked long after the component was first rendered.
benjamn
commented
Aug 20, 2020
| @@ -199,7 +196,32 @@ export function Cart() { | |||
| } | |||
| ``` | |||
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| </ExpansionPanel> | |||
| Alternatively, you can read directly from a reactive variable using the `useReactiveVar` hook introduced in Apollo Client 3.2.0: | |||
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@StephenBarlow Is it okay to refer to an Apollo Client version number in the docs like this?
glasser
approved these changes
Aug 20, 2020
| // to the original elements of the set before we begin iterating. See | ||
| // iterateObserversSafely for another example of this pattern. | ||
| function consumeAndIterate<T>(set: Set<T>, callback: (item: T) => any) { | ||
| const items: T[] = []; |
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You have every reason to expect that to work, but TypeScript complains:
Type 'Set<T>' is not an array type or a string type. Use compiler option '--downlevelIteration' to allow iterating of iterators. [2569]
The ugly truth is that --downlevelIteration adds overhead to all ...spread operations (even the Array-only ones), so that's unfortunately not an option for us, until we're comfortable dropping support for Internet Explorer.
Merged
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This PR implements a React hook called
useReactiveVar(requested in #6818), which can be used to read from a reactive variable in a way that allows the React component to rerender if/when the variable is next updated.Previously, the only way for a reactive variable to trigger a React component rerender was through the use of
useQuery. As the tests included in this PR demonstrate, you don't have to be usinguseQuery(or GraphQL at all) to benefit from the reactivity thatReactiveVar<T>provides.Implementing
useReactiveVarrequired generalizing theReactiveVar<T>API to allow arbitrary listeners (not justInMemoryCacheobjects),but fortunately the existing cache broadcast logic fits nicely within the new listener API(this unification was reverted after discussion with @glasser below).