React Lifecycle Methods: A Guide for Developers

Great web applications that have dynamic user interfaces for use ReactJS. One of its distinguishing features is its component-based architecture, which enables developers to disassemble complicated UI components into smaller, reusable bits. Yet, One needs to manage a component’s behavior at particular phases of its life cycle frequently when dealing with React components. React lifecycle methods are useful in this situation. We will see how to optimize React lifecycle methods to increase the performance of our apps.

What are React Lifecycle Methods?

Let’s first examine lifecycle methods and how they function in ReactJS before moving on to optimization strategies. A component uses methods at particular stages. We call these methods lifecycle methods. Initialization, mounting, updating, and unmounting are some of these method phases. You can manage what occurs at each step to the distinct set of methods that are called at each one.

Throughout a component’s life cycle, the component uses React lifecycle methods in various phases. These techniques allow developers to regulate and modify the behavior of their components during all phases of their life cycles.

The lifecycle of a React component has multiple stages. Each stage uses a set of methods at various times throughout the component’s existence. For designing React components that are effective and efficient, understanding these techniques is crucial.

The Phases

Initialization (Mounting) phase is the first phase of a component’s lifecycle. The component forms at this point, it also configures its basic state and event handlers. At this point, the constructor() function configures the component.

The update phase comes next. The component receives fresh props during this phase, and it modifies its state accordingly. Before rendering, the component uses the getDerivedStateFromProps() function to update the state depending on any changes to the props. To decide whether the component needs to update, the component uses the shouldComponentUpdate() function. The component updates and uses the render() function to return the JSX markup that makes up the component if it returns true.

The component moves into the post-rendering phase after rendering. The componentDidUpdate() function is invoked after the component has updated and the DOM has been altered, whereas the getSnapshotBeforeUpdate() method is used to record information about the DOM before it changes.

The component is deleted from the DOM to complete the unmounting stage. Just before the component is unmounted, the componentWillUnmount() function is invoked.

Once a component is mounted, the componentDidMount() function is invoked (i.e., added to the DOM). Typically, this function is used to set up any external libraries or to retrieve data from an API.

Best Practices for Optimizing React Lifecycle Methods

Now that we understand what lifecycle methods are and how they work, let’s explore some key optimization techniques that can be applied to these methods:

Mounting

constructor()

Use constructor() for initializing state and binding event handlers:

The constructor() method is the best place to initialize state and bind event handlers. Initializing the state in the constructor() ensures that the state is properly set before the component is mounted, which can prevent unnecessary re-renders. Here’s an example:

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      count: 0
    };
    this.handleClick = this.handleClick.bind(this);
  }

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

  render() {
    return (
      <div>
        <h1>{this.props.title}</h1>
        <p>Count: {this.state.count}</p>
        <button onClick={this.handleClick}>Increment</button>
      </div>
    );
  }
}

In this example, the handleClick() function is bound to the component instance, and the initial state is set using the constructor() method. By doing this, the handleClick() method has sufficient access to this.state and this.props.

getDerivedStateFromProps()

Use getDerivedStateFromProps() to update the state based on props: getDerivedStateFromProps() is a lifecycle method that the component calls before rendering and allows you to update the state based on changes to props. This can be useful in situations where you need to keep the component’s state in sync with its props. Here’s an example:

class MyComponent extends React.Component {
  static getDerivedStateFromProps(props, state) {
    if (props.prop1 !== state.prop1) {
      return { prop1: props.prop1 };
    }
    return null;
  }

  constructor(props) {
    super(props);
    this.state = {
      prop1: props.prop1
    };
  }

  render() {
    return (
      <div>
        <h1>{this.props.title}</h1>
        <p>Prop 1: {this.state.prop1}</p>
      </div>
    );
  }
}

In this example, when prop1 changes, we use getDerivedStateFromProps()to update the component’s state. This prevents needless re-renders by ensuring that the component’s state and its props remain in sync.

componentDidMount

This component calls this method immediately after it mounts (i.e. after it inserts into the DOM). In performing any necessary setup, such as initializing a state, fetching data from an API, or adding event listeners, etc, the component uses this method

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      data: []
    };
  }

  componentDidMount() {
    fetch('https://api.example.com/data')
      .then(response => response.json())
      .then(data => {
        this.setState({ data });
      });
  }

  render() {
    return (
      <div>
        <h1>{this.props.title}</h1>
        <ul>
          {this.state.data.map(item => <li key={item.id}>{item.name}</li>)}
        </ul>
      </div>
    );
  }
}

We use componentDidMount() in this example to obtain data from an API and then change the state of the component. We make sure that this process only takes place once (when the component is initially mounted) by executing it in componentDidMount() instead of re-rendering it all the time.

Updating

shouldComponentUpdate()

Use shouldComponentUpdate() to optimize rendering:

Before rendering, the component calls this function shouldComponentUpdate(), giving you the option to decide whether the component should redraw or not. Every time a component’s state or properties change, ReactJS re-renders it by default. If the changes to the state or props are minor, you might wish to avoid performing a new render in some circumstances. As an illustration, consider the following:

class MyComponent extends React.Component {
  shouldComponentUpdate(nextProps, nextState) {
    if (nextProps.prop1 === this.props.prop1 && nextState.count        === this.state.count) {
      return false;
    }
    return true;
  }

  constructor(props) {
    super(props);
    this.state = {
      count: 0
    };
    this.handleClick = this.handleClick.bind(this);
  }

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

  render() {
    return (
      <div>
        <h1>{this.props.title}</h1>
        <p>Count: {this.state.count}</p>
        <button onClick={this.handleClick}>Increment</button>
      </div>
    );
  }
}

In this example, the component uses the shouldComponentUpdate() to avoid needless re-renders while prop1 and count remain constant. When these criteria satisfy, we prevent the component from re-rendering, which might enhance performance, by returning false.

Unmounting

componentWillUnmount()

This component calls this method immediately before it unmounts (i.e., is removed from the DOM). Necessary cleanups, such as removing event listeners or canceling any unresolved API requests, etc use this method.

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      data: []
    };
    this.handleScroll = this.handleScroll.bind(this);
  }

  componentDidMount() {
    window.addEventListener('scroll', this.handleScroll);
  }

  componentWillUnmount() {
    window.removeEventListener('scroll', this.handleScroll);
  }

  handleScroll() {
    // handle scroll event
  }

  render() {
    return (
      <div>
        <h1>{this.props.title}</h1>
        <p>Content goes here</p>
      </div>
    );
  }
}

To remove an event listener that was added in componentDidMount in our example, we are using componentWillUnmount() (). By ensuring that the event listener terminates when the component unmounts, the method helps avoid any memory leaks or issues that may happen if the listener remained active after the component unmounts.

Others

memoization

Use memoization to optimize expensive computations:

Memoization is a technique where you cache the result of an expensive computation so that you quickly retrieve it in the future. In ReactJS, you can use React.memo() higher-order component to memoize the rendering of a component based on its props. Here’s an example:

function ExpensiveComponent({ prop1, prop2 }) {
  const result = useMemo(() => {
    // perform expensive computation based on prop1 and prop2
    return someResult;
  }, [prop1, prop2]);

  return (
    <div>
      <h1>{result}</h1>
    </div>
  );
}

export default React.memo(ExpensiveComponent);

In this illustration, we’re doing a costly computation based on props 1 and 2 using the useMemo() hook, and then memoizing the outcome with React.memo(). As a result, the component avoids unnecessary re-renders and the costly computation only executes when either prop1 or prop2 changes.

Conclusion

In creating web apps, ReactJS is a strong and adaptable toolkit, but to maximize efficiency, it’s crucial to comprehend how its lifecycle methods operate. By adhering to best practices when utilizing lifecycle methods, you however make sure that you carry out costly operations at the appropriate time and that your components only re-render when necessary. You may create web apps that run well, are responsive, and offer a fantastic user experience using these methods.

If you like this blog, you may also like to read about React Custom Hooks