Component Composition Patterns

1. Introduction

Component Composition Patterns are essential design strategies for building scalable and maintainable user interfaces in modern UI frameworks. These patterns dictate how components can be combined to create complex UI structures efficiently.

2. Key Concepts

• **Composition**: The practice of combining simple components to form more complex ones.
• **Separation of Concerns**: Keeping distinct functionalities separate to enhance maintainability.
• **Reusability**: Designing components in a way that they can be reused throughout the application.

3. Types of Composition

There are several composition patterns commonly used in modern UI frameworks:

1. Container/Presentational Pattern: Separates logic from UI rendering.
2. Higher-Order Components (HOCs): Functions that take a component and return a new component with additional functionalities.
3. Render Props: A technique for sharing code between React components using a prop that is a function.
4. Compound Components: Allows components to work together without a strict hierarchy.

3.1 Container/Presentational Pattern

This pattern divides components into two categories:

• Container Components: Handle logic and state management.
• Presentational Components: Focus on UI rendering.

function UserContainer() {
    const [users, setUsers] = React.useState([]);

    React.useEffect(() => {
        fetchUsers().then(setUsers);
    }, []);

    return ;
}

function UserList({ users }) {
    return (
        

            {users.map(user => 
{user.name}
)}
        
    );
}
            

3.2 Higher-Order Components

function withLoading(Component) {
    return function WithLoadingComponent({ isLoading, ...props }) {
        if (isLoading) {
            return 
Loading...
;
        }
        return ;
    };
}

const UserListWithLoading = withLoading(UserList);
            

3.3 Render Props

class DataFetcher extends React.Component {
    state = { data: null };

    componentDidMount() {
        fetchData().then(data => this.setState({ data }));
    }

    render() {
        return this.props.render(this.state.data);
    }
}

 (data ?  : 
Loading...
)} />
            

3.4 Compound Components

Compound components share an implicit state and allow for more flexible component structures.

function Accordion({ children }) {
    const [openIndex, setOpenIndex] = React.useState(null);

    const toggle = index => {
        setOpenIndex(openIndex === index ? null : index);
    };

    return (
        

            {React.Children.map(children, (child, index) =>
                React.cloneElement(child, { isOpen: openIndex === index, toggle: () => toggle(index) })
            )}
        
    );
}

function AccordionItem({ isOpen, toggle, children }) {
    return (
        

            {children[0]}
            {isOpen && 
{children[1]}
}
        
    );
}

// Usage

    Item 1
    Item 2

            

4. Best Practices

To effectively implement component composition patterns, consider the following best practices:

• Design components to be reusable and composable.
• Keep components small and focused on a single responsibility.
• Utilize prop-types to enforce the types of props passed to components.
• Document component behavior and usage for better maintainability.

5. FAQ