hooksintermediate

Rules of Hooks

Hooks must only be called at the top level of React function components or custom hooks.

Mental Model

"The Assembly Line: Every car on the conveyor belt must receive parts in the exact sequential order without skipping stations."

Interactive Engine Simulation

Fiber Hooks Linked List

useState

"Initial"

useEffect

"Idle"

Invariant:The stability of this sequence is what allows React to persist state across asynchronous render cycles.

Executable Code Snippet

Component.jsx

JSX / React 19

1// ❌ ERROR: Hook inside condition
2if (loggedIn) {
3  useEffect(() => { ... });
4}
5
6// ✅ CORRECT: Condition inside hook
7useEffect(() => {
8  if (loggedIn) { ... }
9}, [loggedIn]);

Technical Takeaways & Best Practices

01.Component re-renders are triggered by state or prop changes.
02.Reconciliation algorithm diffs the Virtual DOM to minimize actual DOM updates.
03.Automatic batching optimizes multiple state updates into a single render cycle.

01. Fixed Call Order

React relies on the **order** in which Hooks are called. Internally, it treats hooks as a linked-list. If you skip a hook because of an `if` statement, the pointers for every subsequent hook will shift, returning the wrong state to the wrong variables.

Internal Pointer Fail

Hook A

MISSING

Hook C (Shifted)

02. Only Call in React

Hooks can only be called from **React function components** or **Custom hooks**. They cannot be called from regular JavaScript functions. This is because hooks require access to the "dispatcher" of the currently rendering component instance.

Maintainability Note

"Use the 'eslint-plugin-react-hooks' tool in your IDE. It will automatically catch violations of these rules before you ever run your code. In the Cosmos, laws are enforced by linting."