use state in react in javascript

To use state in React, you first need to define a state object in your component's constructor function. The state object can contain multiple key-value pairs, where each key represents a particular piece of data that you want to store and render.


index.tsx
import React, { Component } from 'react';

class MyComponent extends Component {
  constructor(props) {
    super(props);
    this.state = {
      count: 0,
      message: "Hello World",
      isShowing: false
    };
  }
  // ...
}
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Once you have defined the state object, you can access it and render its values in your component's JSX by using curly braces { }.


index.tsx
class MyComponent extends Component {
  // ...
  render() {
    return (
      <div>
        <h1>{this.state.message}</h1>
        <p>{this.state.count}</p>
        <button onClick={() => this.setState({ count: this.state.count + 1 })}>
          Increase Count
        </button>
      </div>
    );
  }
}
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To update the state object and trigger a re-render of the component, you need to use the setState method. This method takes an object as an argument, where each key corresponds to a state value that you want to update.


index.tsx
class MyComponent extends Component {
  // ...
  handleClick = () => {
    this.setState({ isShowing: !this.state.isShowing });
  };

  render() {
    return (
      <div>
        {this.state.isShowing && <p>{this.state.message}</p>}
        <button onClick={this.handleClick}>
          {this.state.isShowing ? "Hide Message" : "Show Message"}
        </button>
      </div>
    );
  }
}
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In the above example, the handleClick function updates the isShowing state value by toggling its value each time the button is clicked. This in turn will trigger a re-render of the component, and conditionally render the message value based on the current state.

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