From Class to Functional: Migrating to React 18 Hooks

Anton Ioffe - November 20th 2023 - 9 minutes read

In the vibrant ecosystem of React development, the advent of hooks in version 18 has sparked a paradigm shift, beckoning developers to modernize their approach to building components. This article invites seasoned developers to embark on a transformative journey from the familiar terrain of class components to the dynamic landscape of functional components empowered by hooks. We'll dissect classic patterns, pave new pathways with foundational hooks such as useState and useEffect, venture into the depths with advanced hooks, reimagine lifecycle methods, and craft strategies for migrating codebases. Fuse your expertise with the cutting-edge practices delineated herein to redefine the architecture of your React applications, achieving enhanced simplicity, reusability, and performance that hooks are designed to deliver.

Deconstructing Class Components in a Hooks Paradigm

In traditional class components, developers are often required to grapple with the intricacies of the this keyword. A common hurdle is ensuring that this within callback functions refers to the component instance, which necessitates explicit binding of event handlers in the constructor or using class property arrow functions. This requirement often leads to verbose and boilerplate-heavy code that can obfuscate the component's intent. Consider the following example:

class ShowCount extends React.Component {
    constructor(props) {
        this.state = { count: 0 };
        this.handleClickEvent = this.handleClickEvent.bind(this);

    handleClickEvent() {
        this.setState({ count: this.state.count + 1 });

    render() {
        return (
            <label onClick={this.handleClickEvent}>
                Count: {this.state.count}

The need for binding not only adds complexity but also diverts the developer's attention from the actual business logic. Contrast this with functional components using hooks, where such bindings are unnecessary, as functions naturally capture the state without losing context:

function ShowCount() {
    const [count, setCount] = React.useState(0);

    function handleClickEvent() {
        setCount(count + 1);

    return (
        <label onClick={handleClickEvent}>
            Count: {count}

Another aspect where class components introduce complexity is the lifecycle methods. A large class component often spreads logic across different lifecycle methods like componentDidMount, componentDidUpdate, and componentWillUnmount. This dispersion of logic makes it difficult to encapsulate and manage related behaviors. With hooks, related logic can stay cohesively in the same place, enhancing readability and maintainability.

Additionally, testing class components can be cumbersome due to their reliance on the lifecycle methods and stateful behavior, which may require mocking or complex setup in test environments. Hooks promote better testability as the stateful logic gets decoupled from the components, enabling developers to test logic in isolation without mounting the entire component tree.

Understanding these divisions is crucial for developers looking to adopt hooks, as it lays the foundation for recognizing the benefits of modularity and reusability that hooks facilitate. As such, when reassessing class components, a developer's intent should be to distill functionality to its essence, aiming for leaner, more predictable, and encapsulated code constructs that thrive in the hooks paradigm. This paradigm shift isn't just about syntax changes; it's about embracing a mindset that values clear separation of concerns and a more declarative approach to component logic.

The Hooks Transformation: useState and useEffect in Action

In the realm of React development, the advent of hooks has significantly altered the management of state and side-effects in functional components. The useState hook serves to initialize and update local state, while the useEffect hook handles side-effects akin to lifecycle methods found in class components. By utilizing useState, developers declare stateful variables in a functional component without needing a constructor. For instance:

const [count, setCount] = useState(0);

Here count is the stateful variable, and setCount is the method to update it. One common mistake is trying to mutate count directly (e.g., count++), which won't re-render the component. Instead, one should always use setCount to ensure the component reacts to state changes:

setCount(previousCount => previousCount + 1);

The useEffect hook amalgamates the component lifecycle into a single API. Traditional lifecycle methods (componentDidMount, componentDidUpdate, and componentWillUnmount) can now be executed in a single useEffect call by passing an array of dependencies. An empty dependency array [] indicates the effect runs once after the initial render, emulating componentDidMount:

useEffect(() => {
    // Code runs on mount
    return () => {
        // Cleanup code runs on unmount
}, []);

A typical error with useEffect is neglecting the dependencies array, leading to effects running more often than necessary, which might result in performance issues. Conversely, specifying the wrong dependencies can cause stale state issues. It's essential to understand that every value referenced inside the useEffect that might change over time should be included in the dependencies array.

Leveraging these hooks correctly also involves managing state updates that rely on the previous state. Updating state directly, rather than using the previous state passed by the setter function, can lead to outdated state references:

// Incorrect
setCount(count + 1);

// Correct
setCount(previousCount => previousCount + 1);

Handling objects or arrays with useState necessitates spreading the previous state before making updates to avoid losing other state properties:

const [form, setForm] = useState({ name: '', email: '' });

// To update only 'name', we must spread the previous state to retain 'email'
setForm(prevForm => ({ ...prevForm, name: 'New Name' }));

These hooks substantively improve React's functional components by streamlining state and effects management. However, developers should wield them with care to sidestep common pitfalls and thus create efficient and reliable applications.

Advanced Hooks: Beyond Basics to Custom Hooks

Diving into more advanced hooks, useCallback and useMemo serve as effective tools for optimizing performance, particularly when dealing with expensive functions and computations. The useCallback hook returns a memoized callback, preventing the function from being recreated unless certain dependencies change. This mirrors the concept of shouldComponentUpdate, allowing developers to control component re-renders and prevent unnecessary renders when props or state haven't changed significantly. Similarly, useMemo tackles the challenge by memoizing values, ensuring heavy computational functions aren’t needlessly run on every render, a task which previously relied on patterns of memoization and component update blocking.

Harnessing useReducer is an enthralling quest for managing complex state logic. It acts as a more structured alternative to useState for handling state transitions, which is particularly advantageous in scenarios with complex state shapes or when the next state depends intricately on the previous one. The hook simplifies state management within functional components, borrows concepts from Redux-like patterns, and lends itself to cleaner and more predictable state updates.

Custom hooks open a new chapter in the story of React development, offering an unprecedented layer of abstraction and reusability. A well-composed custom hook can be thought of as a container for shareable stateful logic that can be easily transported across different components. These encapsulated functionalities not only trim down the boilerplate but also foster a DRY (Don't Repeat Yourself) codebase. The useIsMobile custom hook, for example, could encapsulate the logic for tracking window size and provide a mobile state indication without wedging in higher-order components or render props.

Reimagine the modular architecture of your React applications by authoring custom hooks, as they are poised to replace intricate patterns like higher order components (HOCs) or render props. Such hooks enable developers to inject shared logic without altering the component hierarchy, safeguarding the principle of separation of concerns. Custom hooks can magnify testability and maintainability by disentangling stateful logic from UI components, which in turn streamlines the transition from monolithic class components to more granular functional compositions.

Reflecting on the potential of advanced and custom hooks, ponder the opportunities for abstracting away complex state interactions and side effects. How could your existing components benefit from a hook-centric redesign? Could the mechanisms provided by useCallback, useMemo, or useReducer offer performance and readability gains? Introducing custom hooks into your codebase requires a strategic mindset; consider the balance between abstracted logic and direct component readability. Remember, with great power comes great responsibility—implement these patterns judiciously to avoid over-engineering and maintaining clarity within your code.

Lifecycle Methods Reimagined: Convert and Refactor with Hooks

In the class-based ecosystem, componentDidMount represented a clear entry point for interactions with the DOM or APIs after a component was inserted into the DOM. To reimagine this lifecycle method with hooks, we utilize the useEffect hook, providing it with an empty dependency array. This pattern ensures the encapsulated operations only run once after the initial render, effectively mirroring the componentDidMount. Beware, though, mistakenly including variables that change over time in the dependency array could lead to redundant API calls or event listeners, causing performance degradation.

useEffect(() => {
    // Actions performed on component mount

    // Cleanup function runs on component unmount
    return () => {
}, []);

The transition from componentDidUpdate requires careful dependency tracking. This hook fires after every render, but with optimized dependencies, you can target updates to state or props changes. A common blunder is introducing unnecessary useEffect invocations by failing to specify dependencies or adding superfluous ones. To align with the precision of componentDidUpdate, include relevant props and state variables as dependencies to refine when the effect should run, preventing unintended execution paths. Correctly mapped dependencies help avoid stale state or props, ensuring the functional parity with the class-based approach.

useEffect(() => {
    // Actions performed on component update with specific dependencies
}, [dependentValue]);

Similarly, componentWillUnmount gets reworked into the cleanup function returned from useEffect. Here lies a frequent source of leaks: neglecting to return a cleanup function within effects that set up subscriptions or event listeners. Providing a return statement with cleanup logic guarantees that side effects are disposed of appropriately, just as componentWillUnmount would in the class-based lifecycle.

In optimizing these hooks, one must thread the needle carefully between under- and over-involvement of dependencies. Excess can lead to unwanted re-renders, while sparsity risks outdated closures over variables. The intensive contraction of lifecycle methods into effects should not neglect due consideration of when and why each effect operates; maintain a balance to prevent overfetching and ensure state coherence.

Reflect on these questions: Are the dependencies within your useEffect hook inclusive of all factors that should induce re-execution? Could any state updates be batched to reduce the number of re-renders? From an architectural perspective, how might the granularity of your components influence the complexity of lifecycle logic with hooks? Continuous introspection on these elements can raise the standard of your refactoring process from class-based to functional reactivity with hooks, aligning with the modern principles of React development.

Strategies and Best Practices for the Migration to Hooks

When embarking on the journey to incorporate Hooks into existing React projects, one sound strategy is the incremental adoption, which mitigates risk and eases the learning curve. Initially, identify simple stateless class components that could benefit from a conversion to functional components with Hooks. This focused scope allows for smaller, more manageable changes and provides a sandbox for developers to gain familiarity with the Hooks API. Remember, wholesale migration is rarely recommended, as it introduces significant risk and disruption; instead, prioritize components that will gain the most immediate benefit from conversion, such as those with tangled lifecycle methods that can be simplified with useEffect.

Another vital consideration is the wrapping of class components with functional components that utilize Hooks. This approach preserves the existing hierarchy and logic of class components while enabling the use of Hooks' features. It's particularly useful when dealing with complex class components that manage substantial state and lifecycle interactions. By wrapping these classes, we maintain backward compatibility and can incrementally replace or update the internal logic as our comfort with Hooks grows. However, this can introduce a layer of indirection that should be carefully considered against the potential benefits.

Optimizing performance should remain a priority when refactoring components. Keep a vigilant eye on potential pitfalls—such as the misuse of dependency arrays in useEffect—that may lead to unnecessary re-renders or stale state. Profiling tools such as React DevTools are indispensable in identifying performance regressions during the migration process. Seek to ensure that converted components are not only functionally equivalent to their class-based predecessors but also as performant, if not more so.

Best practices dictate that backward compatibility should guide the migration process. This is achieved by thoroughly testing refactored components in isolation and within the context of their real-world use cases. Automated testing plays a crucial role here; ensure that unit and integration tests are updated to reflect the new structure and logic of Hooks-based components. It's not merely a matter of ensuring that components work as expected but that they continue to work in harmony with the rest of the application.

In conclusion, the appropriate use of React's robust hook system promotes cleaner code, enhances reusability, and streamlines the state and effect management within functional components. However, developers must navigate the refactoring process with careful forethought and a strategic plan. While piecemeal adoption may appear slower, it is a deliberate, measured process that prioritizes the stability and performance of the application. What edge cases could threaten this stability during conversion, and how can they be preemptively addressed? These are the kinds of questions that should shape the development of your migration strategy.


This article discusses the paradigm shift brought about by React 18 hooks and provides guidance for senior-level developers who want to migrate from class components to functional components using hooks. The article explores the benefits of hooks, such as simplicity, reusability, and improved performance, and delves into topics such as deconstructing class components, using useState and useEffect hooks, advanced hooks like useCallback and useMemo, custom hooks, and the reimagining of lifecycle methods. The article also offers strategies and best practices for migrating to hooks. A challenging technical task for the reader to consider is to identify and convert simple stateless class components to functional components with hooks in an incremental and controlled manner, while ensuring backward compatibility and optimizing performance.

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