Lifecycle Methods in React
Last updated 4th.Dec.2023
Understanding the React component lifecycle is crucial for developers working on React applications. It provides the ability to manage and alter components at various stages, spanning from creation to destruction. The lifecycle comprises several methods that correspond to different phases in a component’s existence. Grasping the interactions between these methods is essential for crafting code that is both efficient and easy to maintain.
In this article, we’ll delve into the significance of the React Component Lifecycle, elucidating why it holds importance and demonstrating effective utilization of its diverse methods in your application development workflow.
About The Author
Sai Ram Soma Having 12+ years of IT experience in React JS & Native, JavaScript, Typescript. Working in a startup from day one. Accustomed to learning and keeping up with the current trend. Experience in developing feature rich web applications using React JS. Experience in developing mobile applications in Android, React Native.
What are React Components?
In a React application, the fundamental building block is a component, which developers utilize to compartmentalize code and isolate different parts of the application.
Components can be broadly categorized into two groups:
Class Components: These components inherently manage the component lifecycle and state.
Functional Components: They are simple, quick to create, and are stateless by default.
Each React class component possesses a lifecycle, essentially representing the component’s state. This lifecycle logic is predefined and provided by React (as class components inherit from React. Component), enabling the handling of events in each stage of a component’s life cycle. The component’s life cycle consists of three stages: Mounting, Updating, and Unmounting.
What are the Lifecycle Methods in React?
Lifecycle methods in React are specialized functions that get called at specific points in a component’s life cycle. They offer a way to hook into the various phases of a component’s existence, from its initial mounting on the DOM to its eventual unmounting and destruction. These methods provide developers with opportunities to perform specific actions like manipulating the state, fetching data, or manually manipulating the DOM at different stages in the component’s life.
The lifecycle of a React component is typically divided into four main phases:
- Initialization
- Mounting
- Updating
- Unmounting
Within each React lifecycle phase, there exist various lifecycle methods that can be customized to execute code at designated points in the process. Collectively, these are referred to as component lifecycle methods.
The diagram depicted below illustrates the React lifecycle methods aligned with the Initialization, Mounting, Updating, and Unmounting phases.
Each of these stages serves a distinct purpose in the development cycle, offering a diverse set of operations to be performed.
Stages of ReactJS Lifecycle?
ReactJS finds applications not only in web development but also extends its utility to IoT and AI domains. Engineers, to construct forms efficiently, should adhere to a structured approach guided by the ReactJS lifecycle, spanning from initialization to unmounting. This approach enhances the scalability of ReactJS applications by leveraging improved processing and a more impactful coding architecture. The properties of one state are influenced by the relationships defined within the system.
Initialization
The initialization stage is the foundational phase in the ReactJS life cycle, crucial for developers to grasp. During this phase, a component is created with specified properties and an initial state is established in the component class’s constructor. Developers need to carefully define the ideal properties (props) and the component’s initial state.
Understanding how components are initialized, particularly in terms of state and properties, is vital. This understanding aids in rendering accurate information beyond the basic markup. Implementing this early in the design phase streamlines the coding process.
The JSX primarily relies on three types of data:
- “error”: Displays a standard message for bugs or rendering errors.
- “loading”: Indicates when the application is retrieving API data.
- “users”: Represents critical data fetched from the API.
This knowledge lays the groundwork for a robust coding architecture within the user interface module. While the initial state is set in the constructor, it can be modified later using the setState method, offering coding flexibility as one progresses through the lifecycle. Additionally, defaultProps is defined to establish default prop values, which can be subsequently overridden with new values.
Setting default values is also crucial, as they provide a foundational state reusable across multiple applications. Getting this part right is key, as it sets the tone for subsequent stages in the lifecycle.
Mounting
The initial phase in the React component lifecycle is Mounting, indicating that a component has been placed onto the DOM tree.
In this stage, there are five methods arranged in the correct order:
constructor()
This method precedes component mounting and is typically placed at the top of the component structure. It serves for initializing local component state and binding event handler methods.
componentWillMount()
Invoked just before the render method, it is often utilized to set the component state and prevent additional re-renders. Deprecated in React version 17 and replaced by the getDerivedStateFromProps method.
static getDerivedStateFromProps(props, state)
Called just before render(), it is where the state can be set based on initial props. Takes props and state as arguments and returns an object with state changes.
render()
Contains JSX code to be rendered when the component is mounted. Unlike other methods, render() is the only required one and is automatically called by React when props or states change.
componentDidMount()
Invoked after the first render in the DOM. Ideal for operations on the DOM tree, setting up subscriptions, or altering state. While it triggers extra rendering, the screen won’t be refreshed immediately, preventing intermediate state values invoked in the render method from rendering in the browser.
Updating
Following the mounting phase in the React component lifecycle is the updating phase. This phase is crucial as it allows the component to evolve from its initial state throughout its time being mounted.
Updates occur due to changes in either props or state. There are several methods available to manage and respond to these updates, which are executed in the following sequence during a component’s re-render:
shouldComponentUpdate(nextProps, next-state)
This method helps prevent unnecessary re-renders. Although components re-render by default with any change in props or state, this method allows developers to specify conditions for re-rendering. It’s called upon receiving new props or states, with certain exceptions like the component’s first render or when forceUpdate() is invoked.
static getDerivedStateFromProps(props, state)
As in the mounting stage, this method adjusts the state based on incoming props.
render()
Identical to its role in the mounting phase, this is the essential method, required for rendering.
getSnapshotBeforeUpdate(prevProps, prevState)
Executed right before the component’s re-render, this method is often used for capturing data like scroll positions before the update. Its return value is passed as a third parameter to componentDidUpdate.
componentDidUpdate(prevProps, prevState, snapshot)
This method is activated right after the render() method, but not on the initial render. It’s useful for DOM manipulations or handling side effects following changes in the received arguments.
Unmounting
The final phase in a component’s lifecycle is unmounting.
componentWillUnmount()
Triggered right before the component is destroyed, this method serves to clean up tasks, such as removing listeners, and subscriptions, aborting pending requests, and other necessary cleanup operations.
Conclusion
As we progress through the Initialization to Unmounting phases, the React lifecycle offers developers a robust framework. This structured pathway allows components to be easily scaled, providing an organized approach to coding complex user interfaces. Each stage ensures the appropriate amount of information and processing, enhancing user interaction by delivering timely feedback. Following the ReactJS lifecycle facilitates a systematic approach, aiding developers in planning and creating functional, resource-efficient, and user-friendly applications. Knowledge of lifecycle components serves as an invaluable tool, empowering developers to craft exceptional web apps using ReactJs.
FAQ’S
React includes three mounting lifecycle methods for component classes: componentWillMount(), render(), and componentDidMount(). The sequence starts with componentWillMount() being called first, followed by the render() method, and finally, the componentDidMount() method.
To update the DOM, you can employ the componentDidUpdate lifecycle method. This method is invoked after a change in the component’s state or props. It provides an opportunity to update the DOM to reflect the alterations in the state or props.
The lifecycle method used for handling errors in React is componentDidCatch(). This method is invoked when an error occurs during the rendering of a component, in its lifecycle methods, or the lifecycle methods of its child components. It provides an opportunity to gracefully handle errors, log them, and display a fallback UI to users, preventing the entire application from crashing due to an unhandled error in a specific component tree.
In React, certain lifecycle methods have been deprecated due to potential issues with future versions of React, particularly with asynchronous rendering. These deprecated methods are:
- componentWillMount(): Previously used for operations before the initial render, this method has been deprecated because initiating asynchronous operations here can lead to bugs.
- componentWillReceiveProps(): This method was typically used to respond to changes in props before a re-render. It has been deprecated due to its potential to trigger multiple re-renders and its confusing nature.
- componentWillUpdate(): This method was invoked just before rendering when new props or states were received. It has been deprecated because it’s not safe to trigger side effects here.
These 3 methods have been marked as unsafe and are undergoing a deprecation process. These methods, prone to misuse, may lead to issues, especially with the upcoming asynchronous rendering in React.
For updating lifecycle methods, the sequence is as follows:
- static getDerivedStateFromProps(): The initial method invoked during the updating phase.
- shouldComponentUpdate(): Enables control over whether the component should re-render.
- render(): Responsible for rendering the UI.
- getSnapshotBeforeUpdate(): Called just before the most recently rendered output is committed to the DOM.
- componentDidUpdate(): Executed immediately after the component is updated in the DOM.
HTML event handling uses attribute-based syntax and direct binding to HTML elements. React event handling uses JSX with camelCase properties and requires explicit binding in class components. React’s synthetic event system normalizes event objects and provides a consistent bubbling strategy. The syntax, binding methods, and handling of event objects differ between HTML and React.