자바개발자 리엑트 배우기 (state)

In React, "state" refers to a feature that allows components to create and manage their own data. This data can change over time and can affect what is rendered in the browser. State is what allows React components to be interactive and dynamic. When a component's state changes, the component responds by re-rendering.

You can think of state as any data that can change over the lifetime of a component. For example, if you were building a counter component, the current count would be kept in state. When the count increases or decreases (perhaps in response to a button being clicked), the component's state is updated to reflect the new count, and the component re-renders to show this updated count.

State in React is encapsulated, meaning it is local or owned by that specific component. It cannot be accessed or modified outside of that component, unless it is explicitly passed down to child components as props or managed with a state management library like Redux or a context provider.

State can be added in two ways:

1. Class Components: In a class component, state is a property of the component instance. It is typically initialized in the constructor and accessed and updated via this.state and this.setState() respectively.

2. Functional Components: In a functional component, state can be added using the useState hook provided by React. useState returns a pair: the current state value and a function that lets you update the state.

It's important to note that updates to a component's state may be asynchronous, and they do not immediately mutate this.state but create a pending state transition. Accessing this.state after calling this.setState() may potentially return the existing value, not the updated one. Therefore, if you need to use the previous state value to compute the new one, you should pass a function to this.setState(), instead of an object.