New Features

tree shaking

react hook

react fragment

real-time applications

Socket.IO

Context API

context is like a global value

use context.provider, then use this.context to get it

https://codesandbox.io/s/contextdemo-di5x7

React.createContext(defaultValue);

.When React renders a component that subscribes to this Context object it will read the current context value from the closest matching Provider above it in the tree.

Context.Provider

<MyContext.Provider value={/* some value */}>

Context.Consumer

class MyClass extends React.Component {
  static contextType = MyContext;
  render() {
    let value = this.context;
    /* render something based on the value */
  }
}