effector/enforce-exhaustive-useUnit-destructuring

Related documentation

Rule Details

This rule enforces that:

• All properties passed in an object to useUnit must be destructured to prevent implicit subscriptions;
• All elements passed in an array to useUnit must be destructured to prevent implicit subscriptions also.

Object shape

When using useUnit with an object, you must destructure all keys that you pass. Otherwise, unused units will still create subscriptions and cause unnecessary re-renders. TypeScript

// 👍 correct - all properties are destructured
const { value, setValue } = useUnit({
  value: $store,
  setValue: event,
});

// 👎 incorrect - setValue is not destructured but still creates subscription
const { value } = useUnit({
  value: $store,
  setValue: event, // unused but subscribed!
});

// 👎 incorrect - extra is destructured but not passed
const {
  value,
  setValue,
  extra // extra is missing - will be undefined
} = useUnit({
  value: $store,
  setValue: event,
});

Array shape

When using useUnit with an array, you must destructure all elements. Elements that are not destructured will still create subscriptions, leading to implicit re-renders. TypeScript

// 👍 correct - all elements are destructured
const [value, setValue] = useUnit([$store, event]);

// 👎 incorrect - $store is not destructured but creates implicit subscription
const [setValue] = useUnit([event, $store]);
// Component will re-render when $store changes, even though you don't use it!

// 👎 incorrect - event and $anotherStore cause implicit subscriptions
const [value] = useUnit([$store, event, $anotherStore]);
// Component re-renders on $store, event, and $anotherStore changes

Why is this important?

Implicit subscriptions can lead to:

• Performance issues: unnecessary re-renders when unused stores update
• Hard-to-debug behavior: component re-renders for unclear reasons
• Memory leaks: subscriptions that are never cleaned up properly

Examples

Real-world example

import React, { Fragment } from "react";
import { createEvent, createStore } from "effector";
import { useUnit } from "effector-react";

const $store = createStore("Hello World!");
const event = createEvent();

// 👎 incorrect
const BadComponent = () => {
  const { value } = useUnit({
    value: $store,
    setValue: event, // ❌ not used but subscribed!
  });

  return <Fragment>{value}</Fragment>;
};

// 👍 correct
const GoodComponent = () => {
  const { value, setValue } = useUnit({
    value: $store,
    setValue: event,
  });

  return <button onClick={() => setValue("New value")}>{value}</button>;
};

import React, { Fragment } from "react";
import { createEvent, createStore } from "effector";
import { useUnit } from "effector-react";

const $store = createStore("Hello World!");
const event = createEvent();

// 👎 incorrect - implicit subscription to $store
const BadComponent = () => {
  const [setValue] = useUnit([event, $store]); // ❌ $store not used but subscribed!

  return <button onClick={() => setValue("New value")}>Click</button>;
};

// 👍 correct - explicit destructuring
const GoodComponent = () => {
  const [value, setValue] = useUnit([$store, event]);

  return <button onClick={() => setValue("New value")}>{value}</button>;
};

// 👍 also correct - only pass what you need
const AlsoGoodComponent = () => {
  const [setValue] = useUnit([event]); // ✅ no implicit subscriptions

  return <button onClick={() => setValue("New value")}>Click</button>;
};

When Not To Use It

If you intentionally want to subscribe to a store without using its value (rare case), you can disable this rule for that line:

// eslint-disable-next-line effector/enforce-exhaustive-useUnit-destructuring
const { value } = useUnit({
  value: $store,
  trigger: $triggerStore, // intentionally subscribing without using
});

However, in most cases, you should refactor your code to avoid implicit subscriptions.