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Linked Lists: The Hidden Power Behind React Hooks

#react #frontend #computerscience #reacthooks

When studying computer science, some concepts feel abstract or even irrelevant. One of the most misunderstood? Linked lists [1]. Many developers leave college thinking, "I'll never use this in real life." But what if I told you that every time you use React Hooks, you're relying on a linked list?

Let’s explore how.

What Is a Linked List?

A linked list is a fundamental data structure where each element (called a node) holds a value and a reference to the next node. Unlike arrays, which store elements contiguously in memory, linked lists form a chain of nodes, allowing for efficient insertions and removals, especially for dynamic or unknown sizes [1].

Here’s a simple example of a linked list node in JavaScript:

class Node {
  constructor(value) {
    this.value = value;
    this.next = null;
  }
}

// Example: Creating a linked list
const node1 = new Node(1);
const node2 = new Node(2);
node1.next = node2; // Links node1 to node2
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This flexibility makes linked lists ideal for scenarios where data needs to grow or shrink dynamically.

The Problem React Needed to Solve

When React introduced Hooks, it faced a challenge:

How do we track multiple hooks inside a single component without requiring developers to name or manage them explicitly?

React’s solution was to rely on call order, storing hook states in a singly linked list attached to the component’s internal structure. Linked lists are perfect here because they allow React to efficiently append new hooks without resizing or shifting elements, unlike arrays.

Hooks as a Linked List

In React, each component has a Fiber node that manages its state. Hooks are stored as nodes in a singly linked list, anchored to the Fiber’s memoizedState property. Here’s a simplified view:

Component Fiber
   |
   └── memoizedState → Hook1 → Hook2 → Hook3 → null
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Each hook node contains:

{
  memoizedState: someStateValue, // The hook's current state
  next: referenceToNextHook,      // Pointer to the next hook
}
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When React renders a component, it traverses this list in the exact order the hooks are called. This is why hooks cannot be called conditionally [2]—it would disrupt the list’s structure. For example:

// Bad: Conditional hook call breaks the linked list
if (condition) {
  const [value, setValue] = useState(0); // React loses track of hook order
}
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Breaking this rule can cause errors like "Rendered more hooks than during the previous render," as React relies on consistent hook order across renders [2].

Inside React’s Codebase

Curious to see this in action? Check out React’s source code on GitHub, specifically the mountWorkInProgressHook function [3]. This function creates a new hook and links it to the list during the initial render:

// React adds a new hook to the linked list
if (workInProgressHook === null) {
  // First hook in the list
  firstWorkInProgressHook = workInProgressHook = hook;
} else {
  // Append to the end of the linked list
  workInProgressHook = workInProgressHook.next = hook;
}
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On subsequent renders, React reuses this list, ensuring hooks are processed in the same order.

Why This Matters for Frontend Developers

You may not think about linked lists when building UIs, but understanding their role in React can give you an edge:

  • Write better custom hooks: Knowing hooks are stored in a linked list helps you design hooks that respect React’s order-based system.
  • Avoid subtle bugs: Misordering hooks (e.g., calling them in loops or conditionals) can break your app. Use React DevTools to inspect the hook chain and debug order-related issues [4].
  • Appreciate React’s elegance: Linked lists enable React to manage dynamic hook counts efficiently, contributing to its performance and simplicity.

Pro Tip: If you suspect a hook-related bug, open React DevTools, select your component, and check the hook order in the Fiber’s memoizedState to ensure consistency [4].

Beyond React: Linked Lists in Frontend Development

Linked lists aren’t just for React. They power features like browser history navigation (e.g., the back/forward stack) and undo/redo functionality in text editors or design tools. Understanding linked lists equips you to tackle a wide range of frontend challenges.

Want to Dive Deeper into React Hooks?

I recently wrote an article exploring the inner workings of Hooks—from linked lists to side effects.

👉 Hooks Under the Hood: How React Hooks Actually Work [5]

Final Thoughts

Linked lists are alive and well, quietly powering your favorite frontend library. The next time someone questions the relevance of data structures, share this insight to show how foundational concepts drive modern development.

Try experimenting with linked lists yourself—build a simple one in JavaScript or explore React’s source code to see them in action. You’ll be surprised at how often they appear!

References

  1. Introduction to Linked Lists - GeeksforGeeks
  2. Rules of Hooks - React Documentation
  3. React Source Code: mountWorkInProgressHook
  4. Debugging with React DevTools - React Documentation
  5. Hooks Under the Hood: How React Hooks Actually Work

Thanks for reading!

If you found this helpful, follow me @talissoncosta for more frontend deep dives.

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