An Overview of Lifecycle Methods in Reactjs

An Overview of Lifecycle Methods in React.js

React.js is a popular JavaScript package used for developing user interfaces, especially for web applications. One of the core features that make React powerful and flexible is its component-based architecture. Components in React can be thought of as reusable building blocks that encapsulate both the UI and the logic required to manage that UI. Understanding the lifecycle of these components is essential for developers to efficiently manage state, handle events, and optimize performance. In this blog, we'll provide an overview of the lifecycle methods in React.js.



What are Lifecycle Methods?
Lifecycle methods are special functions that get called at different stages of a React component's life. They enable developers to perform certain actions or operations at specific points in the component's lifecycle. The lifecycle methods can be broadly categorized into three phases:



Mounting: The phase when a component is being created and inserted into the DOM.

Updating: The phase when a component is re-rendered as a result of changes in props or state.

Unmounting: The phase when a component is removed from the DOM.



Mounting Phase


During the mounting phase, the following lifecycle methods are called in the following order:

constructor(): This is the first method that gets called when a component is created. It is used to initialize state and bind event handlers.

static getDerivedStateFromProps(): This method is called right before rendering the component and allows it to update its state based on changes in props. It is a rarely used method and has some specific use cases.

render(): This method is responsible for returning the JSX (or elements) that represent the UI of the component. It should be a pure function and not cause any side effects.

componentDidMount(): This is called immediately after the component has been rendered to the DOM. It is often used for performing side effects like fetching data from APIs, adding event listeners, etc.



Updating Phase


The updating phase occurs whenever a component's props or state change. This phase includes the following lifecycle methods:

static getDerivedStateFromProps(): As mentioned earlier, this method is called both during mounting and updating phases.

shouldComponentUpdate(): This method allows developers to optimize performance by controlling whether a component should re-render or not. It returns a boolean value that indicates if the component should update.

render(): Just like in the mounting phase, the render() method is called during updating as well, but only if shouldComponentUpdate() allows the update.

getSnapshotBeforeUpdate(): This method is called right before changes from the virtual DOM are committed to the actual DOM. It allows components to capture some information from the DOM before it potentially changes.

componentDidUpdate(): This method is called after the component has been re-rendered and the changes have been applied to the DOM. It is commonly used for side effects similar to componentDidMount().



Unmounting Phase

The unmounting step is when a component is withdrawn from the DOM. The following method is called during this phase:

componentWillUnmount(): This method is invoked immediately before the component is removed from the DOM. It is used for cleaning up resources like event listeners, timers, or cancelling network requests.


The New Lifecycle in React 17+


In React 17, the introduction of concurrent mode brought changes to how React handles certain lifecycle methods. Some methods like componentWillUnmount() have been deprecated, and new methods have been introduced to better support asynchronous rendering. The new methods are:

static getDerivedStateFromProps(): Similar to the previous lifecycle, it exists in both mounting and updating phases.

render(): Just like before, this method is called during both mounting and updating.

componentDidMount(): Only available in the mounting phase.

componentDidUpdate(): Only available in the updating phase.

getSnapshotBeforeUpdate(): Only available in the updating phase.

componentWillUnmount(): Deprecated and no longer used. Instead, use the new method:

componentWillUnmount(): Introduced in React 17, this method is used for cleanup actions before the component is unmounted.

It's essential to stay up-to-date with the latest React documentation to keep track of any changes in the lifecycle methods.



Conclusion


Understanding the lifecycle methods in React.js is crucial for building efficient and well-organized components. By utilizing these methods effectively, developers can manage state, perform side effects, and optimize performance throughout the component's lifecycle. As React continues to evolve, keeping an eye on any updates or changes to these lifecycle methods is important to ensure that your code remains compatible and efficient.