React State

• State is data that’s internal to a component.

• Props are not to be changed by a component, but state is intended to be changed.

• We should only assign a value to state if it will be updated in our component.

Initializing State

• When creating a stateful class component, you can use a class constructor method to initialize the this.state object.

Ex:

import React from 'react';

class RandomQuote extends React.Component {
  constructor() {
    super();

    const quote = 'May the Force be with you.';

    this.state = { 
      quote: quote 
    };
  }

  render() {
    return (
      <>
        <h2>Random Quote</h2>
        <p>{this.state.quote}</p>
      </>
    );
  }
}

Updating State

• The this.setState method accepts an object containing the state properties to update.

• We should always use the this.setState method to update state rather than setting the this.stateproperty directly. Reassigning this.state alone won’t trigger re-rendering, leaving your component out of sync.

• We only use this.state = {} inside our constructor method

• Because calling the this.setState method triggers a re-render, it should not be called from within the render method, as that would trigger an infinite loop.

Ex:

changeQuote = () => {
  const newQuote= 'My favorite state is non-Newtonian fluid.'

  this.setState({ 
    quote: newQuote 
  });
}