React hooks changed the way we write components, but truly understanding what happens when you call useState or useEffect makes you a stronger developer, better equipped to debug and optimize more effectively.
In this article, I explain clearly and practically how hooks work internally and why the rules surrounding them are so strict. I also include how we apply this knowledge at Q2BSTUDIO, a software development company dedicated to creating custom applications and custom software, specializing in artificial intelligence, cybersecurity, and aws and azure cloud services.
Core idea: React maintains an internal structure per component called fiber that includes a linked list of nodes for each hook. When a component renders, React traverses the hooks in the same order they are called in the code and associates each call with a specific node in that list. Thanks to this model, React can persist state and other data between renders and ensure consistency even in concurrent rendering modes.
How React tracks hook calls: during render, React marks the fiber being processed, resets the work pointer, and, as the component function executes, creates or reuses hook nodes in the linked list. Each node contains data such as state value, effect dependencies, or the cleanup function. The order of calls must be deterministic so that nodes match between renders.
What happens when calling useState: on the first execution, React creates a node with the initial value. The setState function it returns is a closure that queues an update and schedules a new render. On subsequent renders, React retrieves the state from the same node and does not reapply the initial value. Updates can be functional and, in the real implementation, are batched to improve performance.
What happens when calling useEffect: useEffect stores the effect function and the dependency array in its node. After the commit phase, React compares dependencies with a shallow check using Object.is. If they change or it is the first execution, React schedules the effect to run after painting and saves the cleanup function if the effect returns one. Cleanups run before the next effect or when the component unmounts.
Why the rules of hooks matter: React relies on the order and number of hook calls being consistent between renders. Calling hooks conditionally or inside loops causes mismatches in the linked list and errors like Invalid Hook Call. The correct way to condition logic that depends on hooks is to always call the hook and then apply conditionals inside the hook.
Common errors and how to avoid them: stale closures due to missing dependencies in useEffect that cause stale values; overusing state when a derived value suffices and causes unnecessary renders; and considering concurrent rendering where React may run additional renders before confirming the commit. Practical recommendation: include all necessary dependencies, prefer computed values over state when possible, and write idempotent effects.
Custom hooks: a custom hook is simply a function that calls other hooks. It registers in the same linked list and therefore respects the same rules. This allows composing reusable logic, for example encapsulating integration logic with APIs, AI agents, or authentication logic tied to aws and azure cloud services, without breaking the hooks model.
Recap of the lifecycle of a hook call: preparation phase where React prepares the fiber and resets the pointer; execution phase where the component function is called and hooks run in order; tracking where each call links to its node in the list; commit phase where effects are applied after painting; and re-render that reuses the same nodes when there are updates.
Resources and recommended reading: the official React documentation on hooks, advanced articles on useEffect, and the source code of the hooks implementation in the React repository help to go deeper. Additionally, at Q2BSTUDIO we apply these principles to develop robust solutions in artificial intelligence, AI for businesses, AI agents, and business intelligence services such as power bi to improve corporate decision-making.
About Q2BSTUDIO: Q2BSTUDIO is a software development company focused on creating custom applications and custom software adapted to each client's needs. We are specialists in artificial intelligence, cybersecurity, aws and azure cloud services, business intelligence services, AI for businesses, AI agents, and power bi. Our approach combines good engineering practices with experience in secure and scalable architectures to deliver solutions that integrate advanced analytics, AI automation, and security compliance.
Why contact us: if your project requires a custom application that leverages artificial intelligence to improve processes, or you need to strengthen the cybersecurity of an aws or azure cloud ecosystem, at Q2BSTUDIO we design and implement complete solutions. We offer consulting in business intelligence, development of AI agents, and deployments integrated with power bi for real-time visualization and analysis.
Final reflection: understanding how hooks work internally is not just theory. It helps you debug, optimize, and design robust custom hooks, and also make better architectural decisions when building custom software with components that interact with advanced AI, cybersecurity, and cloud services. If you are looking for advice to apply these techniques in your product, Q2BSTUDIO can accompany you throughout the entire cycle, from design to production.
