Hooks’ Macro ☔

Babel Macros for React Hooks automatic memoization invalidation.

• Features
• Roadmap
• Installation
• Usage
• Full reference
  • useAutoMemo
  • useAutoCallback
  • useAutoEffect, useAutoLayoutEffect
• Limitations
• Inspiration
• License

Features

1. Extracts all references used, and adds them to the inputs array.

2. Favors strict correctness over performance, but uses safe optimizations:

   1. skips constants and useless memoization keys;

   2. traverses all functions called or referenced, and appends their dependencies too, removing the need for unnecessary useCallback hooks.

3. By lowering the bar for high correctness, strives to:

   1. make the use of useAutoMemo and useAutoCallback simple and applicable in many more contests;

   2. reduce the overhead of modifying an input’s semantics (for example from a constant to a prop);

   3. reduce to the bare minimum cases of missed inputs — and therefore stale memoizations or effects.

4. Thoroughly tested: 50+ test cases and 100% code coverage.

Roadmap

• Create a debug/trace facility to help debugging stale cache, performance issues.
• Create a escape hatch to signal that a reference should not be part of the inputs array.
• Identify a rule where we can safely add property accesses to the inputs array. Very important when dealing with refs (ref.current).
• Bail out on actual constants (such as primitive literals) Update: Done!
• Warn/error on known non-invariant values (such as literal objects or arrays) — or auto-useAutoMemo them!
• Create a auto() generic macro to be used with other hooks and APIs with the same signature.

Installation

Requires babel-plugin-macros, which is already configured for you if you are using Create React App v2+.

npm install --dev hooks.macro

yarn add --dev hooks.macro

Usage

Replace:

import { useMemo } from 'react';

function MyComponent({ labels }) {
  const myComputation = useMemo(
    () => labels.map(label => label.toUpperCase()),
    [labels],
  );
}

With:

import { useAutoMemo } from 'hooks.macro';

function MyComponent({ labels }) {
  const myComputation = useAutoMemo(() =>
    labels.map(label => label.toUpperCase()),
  );
}

Or even:

import { useAutoMemo } from 'hooks.macro';

function MyComponent({ labels }) {
  const myComputation = useAutoMemo(labels.map(label => label.toUpperCase()));
}

Full reference

useAutoMemo

Exactly like React’s useMemo but automatically identifies value dependencies.

Can be passed a factory function or directly a value, will convert the latter to a function for you.

import { useAutoMemo } from 'hooks.macro';

useAutoMemo(value);
useAutoMemo(() => value);

Both become:

useMemo(() => value, [value]);

useAutoCallback

Exactly like React’s useCallback but automatically identifies value dependencies.

import { useAutoCallback } from 'hooks.macro';

useAutoCallback(() => {
  doSomethingWith(value);
});

Becomes:

useCallback(() => {
  doSomethingWith(value);
}, [doSomethingWith, value]);

useAutoEffect, useAutoLayoutEffect

They work exactly like their standard React counterpart, but they automatically identify value dependencies.

import { useAutoEffect, useAutoLayoutEffect } from 'hooks.macro';

useAutoEffect(() => {
  doSomethingWith(value);
});

Becomes:

useEffect(() => {
  doSomethingWith(value);
}, [doSomethingWith, value]);

Limitations

To make this work I currently needed to pose some limitations. This could change in the future (PR very welcome).

1. Only variables created in the scope of the component body are automatically trapped as value dependencies.

2. Only variables, and not properties’ access, are trapped. This means that if you use obj.prop only [obj] will become part of the memoization invalidation keys. This is a problem for refs, and will be addressed specifically in a future release.

   You can work around this limitation by creating a variable which holds the current value, such as const { current } = ref.

3. Currently there’s no way to add additional keys for more fine grained cache invalidation. Could be an important escape hatch when you do nasty things, but in that case I’d prefer to use useMemo/useCallback directly.

4. Only locally defined functions declarations and explicit function expressions (let x = () => {}) are traversed for indirect dependencies — all other function calls (such as xxx()) are treated as normal input dependencies and appended too. This is unnecessary (but not harmful) for setters coming from useState, and not an issue at all if the function is the result of useCallback or useAutoCallback.

Inspiration

React documentation about useMemo and use*Effect hooks cites: (emphasis mine)

The array of inputs is not passed as arguments to the function. Conceptually, though, that’s what they represent: every value referenced inside the effect function should also appear in the inputs array. In the future, a sufficiently advanced compiler could create this array automatically.

This project tries to cover exactly that: to create the inputs array automatically.

License

MIT