In HTML, form elements such as <input>, <textarea>, and <select>typically
maintain their own state and update it based on user input. When a user
submits a form the values from the aforementioned elements are sent with
the form. With React it works differently. The component containing the form
will keep track of the value of the input in it’s state and will re-render the
component each time the callback function e.g. onChange is fired as the
state will be updated. A form element whose value is controlled by React in
this way is called a “controlled component”.
