react setstate prevstate code example

Example 1: react prevstate

handleClick() {
  this.setState(prevState => ({
    isToggleOn: !prevState.isToggleOn
  }));
}

Example 2: prevstate in usestate

const [prevState, setState] = React.useState([]);

setState(prevState => [...prevState, 'somedata'] );

Example 3: this.setstate prevstate

this.setState(prevState => ({ n: !prevState.n }))

Example 4: prevstate in react

handleClick() {
        this.setState(prevState => {
            return {
                count: prevState.count + 1
            }
        })
    }

Example 5: react setState

this.setState({
      date: new Date()
    });

Example 6: react setState

incrementCount() {
  // Note: this will *not* work as intended.
  this.setState({count: this.state.count + 1});
}

handleSomething() {
  // Let's say `this.state.count` starts at 0.
  this.incrementCount();
  this.incrementCount();
  this.incrementCount();
  // When React re-renders the component, `this.state.count` will be 1, but you expected 3.

  // This is because `incrementCount()` function above reads from `this.state.count`,
  // but React doesn't update `this.state.count` until the component is re-rendered.
  // So `incrementCount()` ends up reading `this.state.count` as 0 every time, and sets it to 1.

  // The fix is described below!
}