In React, both state and props are used to manage data and control the behavior of components, but they serve different purposes and have some key differences.

State:

1. Local to the Component:

  • State is a local/internal data storage available only to the component that owns and sets it.
  • It is initialized in the `constructor` method of a class component.

2. Mutable:

  • State can be updated using the `setState` method, triggering a re-render of the component.
  • Directly mutating state (e.g., `this.state.someProperty = newValue`) will not re-render the component.

3. Managed Internally:

  • State is managed internally by the component and is typically used for data that can change during the component's lifecycle.

4. Async State Updates:

  • The `setState` function can accept a callback, which will be executed after the state is updated.

5. Used for Dynamic Data:

  • State is commonly used for dynamic data that can change over time, such as user input, fetched data, or toggling UI elements.

Props:

1. External Input:

  • Props (short for "properties") are external inputs to a component that are passed to it by its parent component.
  • Props are read-only for the component that receives them.

2. Immutable:

  • Props are immutable. A child component cannot modify the props it receives from its parent.

3. Functional Components:

  • Functional components receive props as a function argument, while class components access them via `this.props`.

4. Used for Passing Data:

  •  Props are commonly used to pass data and event handlers from parent components to child components.

5. Static Configuration:

  • Props are typically used for static configuration of a component, while dynamic behavior is often handled by state.

When to Use State vs Props:

Use State When:

  • You need to manage and update data within the component.
  • The data is expected to change over time.
  • The data is not controlled by a parent component.

Use Props When:

  • You want to pass data from a parent component to a child component.
  • You want to configure a child component with static data.
  • The data is static and does not change within the component.

In many cases, components use both state and props. State is used for managing internal dynamic data, while props are used for passing data and configuration from parent to child components. The combination of stateful and stateless components allows for a flexible and modular design in React applications.