controlled and uncontrolled components React the concept of controlled and uncontrolled components is relative to the form. In React , the form element usually holds the internal state , so it works differently from other HTML elements. The different implementation of state within the form element results in controlled and uncontrolled components. controlled components in the HTML form elements, they usually maintain a set of state and update UI as the user inputs. This behavior is not controlled by our program. If we establish a dependency between the state attribute and the value of the form element in React , then update the state attribute through the onChange event and setState () . You can control what happens to the form during user input. React form input elements that control values in this way are called controlled components. & nbsp; if a input input box is defined in React , it does not have the same bi-directional binding function as v-model in Vue , that is to say, we do not have an instruction to combine the data with the input box, and the user enters the content in the input box, and then the data is updated synchronously. class Input extends React.Component {   render () {     return <input name="username" />   } } when users enter content in the input box on the interface, it maintains a state . This state is not the this.state that we usually see, but the abstract state on each form element, so that we can update the UI according to…