Why React Hooks, and How Did We Even Get Here?

React has come a long way since its initial release in 2013. As a full-stack developer who has worked with React since its early days, I‘ve seen firsthand how its component model has evolved to meet the growing demands of modern web applications.

From mixins to higher-order components to render props, each new pattern has aimed to address the limitations of its predecessor and provide developers with more powerful tools for building reusable and composable UI components. But even with these advancements, React components could still become overly complex and difficult to maintain as applications grew in size and scope.

This is where hooks come in. Introduced in React 16.8, hooks represent a fundamental shift in how we think about and build React components. By allowing you to use state and lifecycle features in function components, hooks offer a more flexible and declarative way to manage stateful logic and side effects.

But to fully appreciate the significance of hooks, it‘s important to understand the history of React component patterns and the specific problems that hooks aim to solve. In this article, we‘ll take a deep dive into the evolution of React‘s component model, the limitations of previous patterns, and why hooks may just be the future of React development.

The Evolution of React Component Patterns

Let‘s start by looking at how React components have evolved over time.

Mixins (2013-2015)

In the early days of React, mixins were the primary way to share code between components. Mixins allowed you to define a set of methods that could be "mixed in" to a component, providing a way to reuse lifecycle hooks and other stateful logic.

Here‘s an example of a mixin that subscribes to window resize events:

const WindowResizeMixin = {
  getInitialState() {
    return { width: window.innerWidth };
  },

  componentDidMount() {
    window.addEventListener(‘resize‘, this.handleResize);
  },

  componentWillUnmount() {
    window.removeEventListener(‘resize‘, this.handleResize);
  },

  handleResize() {
    this.setState({ width: window.innerWidth });
  }
};

class MyComponent extends React.Component {
  mixins: [WindowResizeMixin],
  render() {
    return <div>Window width is {this.state.width}</div>;
  }
}

While mixins were a useful tool, they had several notable limitations:

• Name Clashes: Mixins could easily introduce name clashes, as they all shared the same namespace within a component.
• Implicit Dependencies: Mixins could depend on the presence of certain methods or properties in a component, making it difficult to reason about a component‘s behavior.
• Snowballing Complexity: As more mixins were added to a component, it became increasingly difficult to understand how they interacted and what the final behavior would be.

Due to these issues, the React team eventually discouraged the use of mixins in favor of alternative patterns. By mid-2015, mixins had largely fallen out of favor in the React community.

Higher-Order Components (2015-2018)

To address the limitations of mixins, the React community shifted towards higher-order components (HOCs). An HOC is a function that takes a component and returns a new component with some additional props or behavior.

Here‘s an example of an HOC that provides window width to a component:

function withWindowWidth(WrappedComponent) {
  return class extends React.Component {
    state = { width: window.innerWidth };

    componentDidMount() {
      window.addEventListener(‘resize‘, this.handleResize);
    }

    componentWillUnmount() {
      window.removeEventListener(‘resize‘, this.handleResize);
    }

    handleResize = () => {
      this.setState({ width: window.innerWidth });
    };

    render() {
      return <WrappedComponent width={this.state.width} {...this.props} />;
    }
  };
}

class MyComponent extends React.Component {
  render() {
    return <div>Window width is {this.props.width}</div>;
  }
}

export default withWindowWidth(MyComponent);

HOCs provided several benefits over mixins:

• Prop Namespacing: HOCs could provide props with unique names, avoiding the name clashes common with mixins.
• Explicit Dependencies: The props provided by an HOC were explicitly passed to the wrapped component, making dependencies clearer.
• Composability: HOCs could be composed together, allowing for more flexible and reusable code.

However, HOCs also introduced some new issues:

• Wrapper Hell: Composing multiple HOCs could lead to deeply nested "wrapper hell", making components harder to debug and reason about.
• Naming Collisions: While HOCs avoided the name clashes of mixins, they could still introduce naming collisions with the props of the wrapped component.
• Ref Issues: HOCs didn‘t automatically forward refs to the wrapped component, which could cause issues with certain patterns like focus management.

Despite these limitations, HOCs became the dominant pattern for code reuse in React between 2015 and 2018. Libraries like Redux and React Router heavily relied on HOCs for integrating with React components.

Render Props (2017-2019)

As React continued to evolve, a new pattern emerged to address some of the limitations of HOCs: render props. With render props, a component receives a function as its child and calls it to render its own content.

Here‘s an example of a component that provides window width using a render prop:

class WindowWidth extends React.Component {
  state = { width: window.innerWidth };

  componentDidMount() {
    window.addEventListener(‘resize‘, this.handleResize);
  }

  componentWillUnmount() {
    window.removeEventListener(‘resize‘, this.handleResize);
  }

  handleResize = () => {
    this.setState({ width: window.innerWidth });
  };

  render() {
    return this.props.children(this.state.width);
  }
}

class MyComponent extends React.Component {
  render() {
    return (
      <WindowWidth>
        {width => <div>Window width is {width}</div>}
      </WindowWidth>
    );
  }
}

Render props offered several advantages over HOCs:

• Explicit Dependencies: Like HOCs, render props made dependencies explicit by passing them as arguments to the render function.
• Flexible Composition: Render props allowed for more flexible composition patterns, as the rendering logic was determined by the child function rather than the wrapper component.
• No Naming Collisions: By passing data as arguments to a function, render props avoided the naming collisions common with HOCs.

However, render props still had some notable drawbacks:

• Callback Hell: Composing multiple render props could lead to deeply nested "callback hell", similar to the "wrapper hell" of HOCs.
• Verbose Syntax: Render props could be verbose and harder to read, especially when dealing with multiple levels of nesting.
• Performance Overhead: The use of function children could introduce additional performance overhead, as new functions were created on each render.

Despite these limitations, render props gained significant popularity in the React community between 2017 and 2019. Libraries like React Motion and Downshift leveraged render props heavily for their APIs.

The Rise of Hooks (2019-Present)

Hooks, introduced in React 16.8, aim to address many of the long-standing issues with code reuse and component composition in React. By allowing you to use state and lifecycle features in function components, hooks provide a more flexible and intuitive way to manage stateful logic and side effects.

Here‘s an example of how you could use hooks to subscribe to window resize events:

import { useState, useEffect } from ‘react‘;

function useWindowWidth() {
  const [width, setWidth] = useState(window.innerWidth);

  useEffect(() => {
    const handleResize = () => setWidth(window.innerWidth);
    window.addEventListener(‘resize‘, handleResize);
    return () => window.removeEventListener(‘resize‘, handleResize);
  }, []);

  return width;
}

function MyComponent() {
  const width = useWindowWidth();
  return <div>Window width is {width}</div>;
}

Hooks offer several key benefits over previous patterns:

• Reusability: Custom hooks like useWindowWidth can be easily shared between components without modifying the component hierarchy or introducing new wrappers.
• Flat Component Structure: By allowing you to use state and lifecycle features directly in function components, hooks promote a flatter and more readable component structure.
• Encapsulation: Custom hooks provide a clean way to encapsulate complex stateful logic and side effects, making components easier to understand and test.
• Increased Flexibility: Hooks can be composed and combined in endless ways, allowing for much more flexible code reuse patterns than HOCs or render props.

Since their introduction, hooks have seen rapid adoption in the React community. According to a 2020 survey by the State of JS, 68% of React developers reported using hooks in their projects, compared to just 37% in 2019.

This rapid adoption is due in part to the performance benefits of hooks. By eliminating the need for class components and the associated overhead of this bindings and lifecycle methods, hooks can result in smaller bundle sizes and faster rendering.

For example, the React team reported that rewriting the Facebook Marketplace app with hooks resulted in a 7% reduction in bundle size and a 9% improvement in initial render performance.

Mastering Hooks

While hooks are a powerful tool, they do come with a few rules and best practices to keep in mind:

1. Only Call Hooks at the Top Level: Hooks should only be called at the top level of your function components, not inside loops, conditions, or nested functions. This ensures that hooks are always called in the same order on each render.

2. Only Call Hooks from React Functions: Hooks should only be called from React function components or custom hooks, not from regular JavaScript functions.

3. Use Multiple State Variables: Instead of packing multiple values into a single state object, use multiple calls to useState to keep state variables independent and easier to update.

4. Avoid Stale Closures: Be mindful of stale closures when using hooks like useEffect and useCallback. Make sure to include all necessary dependencies in the dependency array to avoid bugs.

5. Use Descriptive Names: Give your custom hooks descriptive names that reflect their purpose, starting with "use" (e.g., useWindowWidth, useFetch, etc.).

By following these rules and best practices, you can avoid common pitfalls and write clean, maintainable code with hooks.

The Future of React

Hooks represent a major shift in how we think about and build React components. By providing a more flexible and composable way to manage stateful logic and side effects, hooks have the potential to dramatically simplify React development and enable new patterns of code reuse.

As the React ecosystem continues to embrace hooks, we can expect to see a proliferation of custom hooks for various use cases, from data fetching and animation to complex application-specific behaviors. We may also see new tooling and best practices emerge to help manage and optimize hook-based code.

However, it‘s important to remember that hooks are not a replacement for all previous patterns. There are still situations where class components, HOCs, or render props may be a better fit, and it‘s important to choose the right tool for the job based on the specific requirements of your application.

Ultimately, the success of hooks will depend on the React community‘s ability to adopt and scale these patterns in real-world applications. But given the benefits and rapid adoption so far, it‘s clear that hooks are here to stay and will play a major role in the future of React development.

Conclusion

React‘s component model has come a long way since the early days of mixins and class components. Each new pattern, from HOCs to render props to hooks, has aimed to address the limitations of its predecessor and provide developers with more powerful tools for building reusable and composable UI components.

Hooks, in particular, represent a major leap forward in React‘s evolution. By providing a more flexible and intuitive way to manage stateful logic and side effects, hooks have the potential to dramatically simplify React development and enable new patterns of code reuse.

As a full-stack developer who has worked with React for many years, I‘m excited to see how the community adopts and scales these patterns in the coming years. While there will undoubtedly be challenges and growing pains along the way, I believe that hooks are a positive step forward for React and will ultimately lead to more maintainable, performant, and reusable code.

If you‘re new to hooks or still on the fence about adopting them in your projects, I encourage you to give them a try and see for yourself how they can simplify your React code. And if you‘re already using hooks, keep pushing the boundaries of what‘s possible and share your experiences and best practices with the community.

Together, we can continue to evolve React‘s component model and build better, more resilient applications for the web.