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Difference Between State and Props in React.JS

State and Props in React.js

React.js is a popular JavaScript library used for building user interfaces. As a React developer, understanding the concepts of state and props is crucial for creating dynamic and interactive applications. While both state and props serve a similar purpose of managing data in React components, they have distinct differences. In this article, we will delve into the difference between State and Props, and explore their respective use cases.

What is State?

In React, state represents the internal data of a component. It is managed and controlled by the component itself, allowing it to handle changes and updates. The state is declared and initialized within a component’s constructor or using the useState hook (introduced in React 16.8). Changes to the state trigger a re-render of the component, ensuring that the user interface reflects the latest data.

Key points about the State:

  1. State is mutable and can be modified within the component that owns it.
  2. State changes are typically triggered by user interactions, API responses, or timers.
  3. The setState method is used to update the state, which triggers a re-render of the component.
  4. State is local to a component and cannot be accessed or modified from outside the component.

What are Props?

Props, short for properties, are used to pass data from a parent component to its child components. They enable communication and data sharing between components in a React application. Props are immutable, meaning they cannot be changed within the receiving component. The parent component is responsible for updating the props and propagating the changes down the component tree.

Key points about props:

  1. Props are passed from a parent component to a child component.
  2. Props are read-only and cannot be modified within the component that receives them.
  3. Props help in creating reusable components and maintaining a unidirectional data flow.
  4. Changes to props in the parent component trigger updates in the child components that rely on them.

Difference Between State & Props in React.js

State Props
Ownership Owned and controlled by the component internally Passed down from a parent component
Mutability Mutable Read-only and cannot be modified by the child component
Usage Manages component’s internal data Configures and customizes child components based on the parent’s requirements
Updates setState method Updated by the parent component and remain static in the child
Example Counter component managing count state Greeting component receiving name and message props

Declaring and Initializing State in React.js Components

In React.js, the state can be declared and initialized in two ways: using the constructor method or utilizing the useState hook (introduced in React 16.8). Let’s explore each approach:

  1. Constructor Method: In class components, the constructor is used to initialize the state. Within the constructor, we define the initial state object using this.state = { }. This approach is commonly used in React versions prior to 16.8.
  2. useState Hook: In functional components, the useState hook allows us to add a state to functional components. By invoking the hook, we can declare a state variable and its initial value, like this: const [state, setState] = useState(initialValue).

Passing Props from Parent to Child Components

To pass data from a parent component to a child component, we use props. Here’s how it works:

  1. In the parent component, we specify the props by adding attributes to the child component. For example: <ChildComponent propName={propValue} />.
  2. In the child component, we can access the passed props using the props object. For functional components, props are passed as a parameter, while in class components, props are accessible through this.props.

Managing State Changes with setState() Method

React components can update their state using the setState() method. Here’s an overview of the process:

  1. To update the state, we call setState() and pass in the new state object or a function that returns the new state object.
  2. React will merge the new state with the existing state and re-render the component to reflect the changes.
  3. It’s important to note that setState() is asynchronous, so we need to be mindful of any dependencies on the current state when updating it.

Handling Props in Child Components

Child components receive props from their parent components and use them to render content or perform certain actions. Here are some key points to consider when handling props in child components:

  1. Accessing Props: In functional components, props are accessed directly as parameters. In class components, props are accessed via this.props.
  2. Prop Validation: React provides a way to validate props using the propTypes property. This helps ensure that the expected data types and structures are passed to the child component.
  3. Conditional Rendering: Child components can use props to conditionally render different content based on the provided data.

Best Practices for Using State and Props in React.js

To make the most of state and props in React.js, it’s important to follow some best practices:

  1. Keep State Local: It is recommended to keep the state localized to the component that truly needs it. Avoid unnecessary sharing of state across multiple components to maintain better component encapsulation and reusability.
  2. Minimize State Usage: Identify the essential data that needs to be stored in the state. Avoid duplicating data or storing derived data in the state. Instead, calculate derived data within the component based on props or other state values.
  3. Immutable State Updates: React encourages immutable state updates. Instead of modifying the state directly, create a new copy of the state object and modify that. This ensures predictable behavior and helps with performance optimizations.
  4. Lift State Up: When multiple components need access to the same state or when the state affects multiple components, consider lifting the state up to a common parent component. This allows for centralized state management and avoids prop drilling.
  5. Prop Types and Default Values: Use prop types to specify the expected data types of props and provide default values where applicable. This helps catch potential errors and makes your components more resilient.
  6. PureComponent and React.memo: Utilize PureComponent (for class components) and React.memo (for functional components) to optimize rendering. These higher-order components perform shallow equality checks on props to prevent unnecessary re-renders.
  7. Consider Using State Management Libraries: As your application grows in complexity, you might benefit from using state management libraries like Redux or MobX. These libraries provide centralized and predictable state management solutions.

By following these best practices, you can write cleaner and more maintainable React.js code that effectively utilizes state and props.

State vs Props: When to Use Each in React.js

State and props serve different purposes in React.js, and understanding when to use each is crucial for writing efficient and maintainable code. Let’s explore the scenarios where state and props are typically used:


  1. Component-specific Data: The state is ideal for managing data that is internal and specific to a particular component. It represents the component’s private data that can change over time, such as form input values, toggle states, or data fetched from an API.
  2. Local Data Manipulation: If a component needs to perform calculations, sorting, filtering, or any data manipulation that affects only itself, using state is appropriate. The state allows the component to control and update the data without affecting other components.
  3. Triggering Component Updates: When the component’s internal data changes and the UI needs to be re-rendered to reflect those changes, the state comes into play. By updating the state using setState(), React triggers a re-render of the component and its child components.


  1. Data Sharing Between Components: Props are used to pass data from a parent component to its child components. When multiple components need access to the same data, the parent component can pass it down as props, enabling communication and data sharing between components.
  2. Unidirectional Data Flow: React promotes a unidirectional data flow, where data flows from parent to child components. Props facilitate this flow by allowing data to be passed down the component hierarchy, ensuring a predictable flow of information and making the application easier to understand and debug.
  3. Reusability of Components: By using props, components can become reusable building blocks. They can be configured and customized by passing different props, enabling them to render different content or behave differently based on the provided data.
  4. Communication with Parent Components: Props also serve as a means for child components to communicate with their parent components. Child components can invoke callback functions passed as props to notify the parent about events or trigger actions in the parent component.

In summary, use the state for managing component-specific and mutable data, triggering component updates, and local data manipulation. Use props for sharing data between components, enabling reusability, ensuring a unidirectional data flow, and facilitating communication with parent components. By understanding the appropriate use cases for state and props, you can design React applications that are modular, efficient, and easy to maintain.


Understanding the difference between state and props is essential for developing robust React.js applications. While the state manages internal component data and can be modified within the component itself, props are used for passing data from parent to child components and are read-only within the receiving component. By leveraging the power of both state and props, React developers can create highly interactive and dynamic user interfaces.

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