Intuitive magical memoization library with Proxy and WeakMap
npm install proxy-memoize
Intuitive magical memoization library with Proxy and WeakMap
The feature has been pretty stable in v1.
In v2, we added some new capabilities.
Our docs and examples are not very comprehensive,
and we hope to have more best practices.
Contributions are welcome.
Immutability is pivotal in more than a few frameworks, like React and Redux. It enables simple-yet-efficient change detection in large nested data structures.
JavaScript is a mutable language by default. Libraries like immer simplify updating immutable data strucutres.
This library helps deriving data from immutable structures (AKA, selectors), efficiantly caching results for faster performance.
This library utilizes Proxy and WeakMap, and provides memoization.
The memoized function will re-evaluate the original function
only if the used part of argument (object) is changed.
It's intuitive in a sense and magical in another sense.
When it (re-)evaluates a function,
it will wrap an input object with proxies (recursively, on demand)
and invoke the function.
When it's finished it will check what is "affected".
The "affected" is a list of paths of the input object
that are accessed during the function invocation.
Next time when it receives a new input object,
it will check if values in "affected" paths are changed.
If so, it will re-evaluate the function.
Otherwise, it will return a cached result.
The cache size is 1 by default, but configurable.
We have 2-tier cache mechanism.
What is described so far is the second tier cache.
The first tier cache is with WeakMap.
It's a WeakMap of the input object and the result of function invocation.
There's no notion of cache size.
In summary, there are two types of cache:
* tier-1: WeakMap based cache (size=infinity)
* tier-2: Proxy based cache (size=1, configurable)
``bash`
npm install proxy-memoize
`js
import { memoize } from 'proxy-memoize';
const fn = memoize(x => ({ sum: x.a + x.b, diff: x.a - x.b }));
fn({ a: 2, b: 1, c: 1 }); // ---> { sum: 3, diff: 1 }
fn({ a: 3, b: 1, c: 1 }); // ---> { sum: 4, diff: 2 }
fn({ a: 3, b: 1, c: 9 }); // ---> { sum: 4, diff: 2 } (returning a cached value)
fn({ a: 4, b: 1, c: 9 }); // ---> { sum: 5, diff: 3 }
fn({ a: 1, b: 2 }) === fn({ a: 1, b: 2 }); // ---> true
`
Instead of bare useMemo.
`jsx
const Component = (props) => {
const [state, dispatch] = useContext(MyContext);
const render = useCallback(memoize(([props, state]) => (
{/ render with props and state /}
)), [dispatch]);
return render([props, state]);
};
const App = ({ children }) => (
{children}
);
`
Instead of reselect.
`jsx
import { useSelector } from 'react-redux';
const getScore = memoize(state => ({
score: heavyComputation(state.a + state.b),
createdAt: Date.now(),
}));
const Component = ({ id }) => {
const { score, title } = useSelector(useCallback(memoize(state => ({
score: getScore(state),
title: state.titles[id],
})), [id]));
return
* CodeSandbox 1
* CodeSandbox 2
* Hooks & Recipes
$3
The example above might seem tricky to create memoized selector in component.
Alternatively, we can use
option.`jsx
import { useSelector } from 'react-redux';const getScore = memoize(state => ({
score: heavyComputation(state.a + state.b),
createdAt: Date.now(),
}));
const selector = memoize(([state, id]) => ({
score: getScore(state),
title: state.titles[id],
}), {
size: 500,
});
const Component = ({ id }) => {
const { score, title } = useSelector(state => selector([state, id]));
return
{score.score} {score.createdAt} {title};
};
`The drawback of this approach is we need a good estimate of
in advance.Usage with Zustand
For derived values.
`jsx
import { create } from 'zustand';const useStore = create(set => ({
valueA,
valueB,
// ...
}));
const getDerivedValueA = memoize(state => heavyComputation(state.valueA))
const getDerivedValueB = memoize(state => heavyComputation(state.valueB))
const getTotal = state => getDerivedValueA(state) + getDerivedValueB(state)
const Component = () => {
const total = useStore(getTotal)
return
{total};
};
`Usage with immer
Disabling auto freeze is recommended. JavaScript does not support nested proxies of frozen objects.
js
import { setAutoFreeze } from 'immer';
setAutoFreeze(false);
`API
$3
This is to unwrap a proxy object and return an original object.
It returns null if not relevant.
\[Notes]
This function is for debugging purpose.
It's not supposed to be used in production and it's subject to change.
#### Examples
javascript
import { memoize, getUntracked } from 'proxy-memoize';const fn = memoize(obj => {
console.log(getUntracked(obj));
return { sum: obj.a + obj.b, diff: obj.a - obj.b };
});
`$3
This is to replace newProxy function in upstream library, proxy-compare.
Use it at your own risk.
\[Notes]
See related discussoin:
$3
Create a memoized function
#### Parameters
*
function (obj: Obj): Result
* options {size: number?, noWeakMap: boolean?}? *
options.size (default: 1)
* options.noWeakMap disable tier-1 cache (default: false)#### Examples
`javascript
import { memoize } from 'proxy-memoize';const fn = memoize(obj => ({ sum: obj.a + obj.b, diff: obj.a - obj.b }));
`Returns function (obj: Obj): Result
$3
Create a memoized function with args
#### Parameters
*
function (...args: Args): Result
* options Options? *
options.size (default: 1)#### Examples
`javascript
import { memoizeWithArgs } from 'proxy-memoize';const fn = memoizeWithArgs((a, b) => ({ sum: a.v + b.v, diff: a.v - b.v }));
`Limitations and workarounds
$3
js
const fn = memoize(obj => {
console.log(obj.c); // this will mark ".c" as used
return { sum: obj.a + obj.b, diff: obj.a - obj.b };
});
`A workaround is to unwrap a proxy.
js
const fn = memoize(obj => {
console.log(getUntracked(obj).c);
return { sum: obj.a + obj.b, diff: obj.a - obj.b };
});
`$3
js
const fn = memoize(obj => {
return { x: obj.a, y: { z: [obj.b, obj.c] } }; // plain objects
});
`In this case above, the return value is clean, however, see the following.
js
const fn = memoize(obj => {
return { x: new Set([obj.a]), y: new Map([['z', obj.b]]) }; // not plain
});
`We can't unwrap Set/Map or other non-plain objects.
The problem is when
is an object (which will be wrapped with a proxy)
and touching its property will record the usage, which leads
unexpected behavior.
If obj.a is a primitive value, there's no problem.There's no workaround.
Please be advised to use only plain objects/arrays.
Nested objects/arrays are OK.
$3
`js
const fn = memoize(obj => {
return { sum: obj.a + obj.b, diff: obj.a - obj.b };
});const state = { a: 1, b: 2 };
const result1 = fn(state);
state.a += 1; // Don't do this, the state object must be immutable
const result2 = fn(state); // Ends up unexpected result
`The input
or the state must be immutable.
The whole concept is built around the immutability.
It's faily common in Redux and React,
but be careful if you are not familiar with the concept.There's no workaround.
$3
`js
const fn = memoize(obj => {
return { sum: obj.a + obj.b, diff: obj.a - obj.b };
});
`The input
is the only argument that a function can receive.`js
const fn = memoize((arg1, arg2) => {
// arg2 can't be used
// ...
});
`A workaround is to use
util.Note: this disables the tier-1 cache with WeakMap.
Comparison
$3
At a basic level, memoize can be substituted in for
createSelector. Doing
so will return a selector function with proxy-memoize's built-in tracking
of your state object.`ts
// reselect
// selecting values from the state object requires composing multiple functions
const mySelector = createSelector(
state => state.values.value1,
state => state.values.value2,
(value1, value2) => value1 + value2,
);// ----------------------------------------------------------------------
// proxy-memoize
// the same selector can now be written as a single memoized function
const mySelector = memoize(
state => state.values.value1 + state.values.value2,
);
`With complex state objects, the ability to track individual properties
within
means that proxy-memoize will only calculate a new
value if and only if the tracked property changes.`ts
const state = {
todos: [{ text: 'foo', completed: false }]
};// reselect
// If the .completed property changes inside state, the selector must be recalculated
// even through none of the properties we care about changed. In react-redux, this
// selector will result in additional UI re-renders or the developer to implement
// selectorOptions.memoizeOptions.resultEqualityCheck
createSelector(
state => state.todos,
todos => todos.map(todo => todo.text)
);
// ----------------------------------------------------------------------
// proxy-memozie
// If the .completed property changes inside state, the selector does NOT change
// this is because we track only the accessed property (todos.text) and can ignore
// the unrelated change
const todoTextsSelector = memoize(state => state.todos.map(todo => todo.text));
`Related projects
proxy-memoize depends on an internal library proxy-compare.
and valtio are libraries that depend on the same library.memoize-state` provides a similar API for the same goal.