What is the difference between Element and Component?

An element is a plain object describing what you want to appear on the screen in terms of the DOM nodes or other components. Elements can contain other elements in their props. Creating a React element is cheap. Once an element is created, it is never mutated. The object representation of React element would be as follows,

const element = React.createElement(
  'div',
  {id: 'login-btn'},
  'Login'
)

The above createElement returns as object as below,

{
  type: 'div',
  props: {
    children: 'Login',
    id: 'login-btn'
  }
}

And finally it renders to the DOM using ReactDOM.render as below,

<div id='login-btn'>Login</div>

Whereas a component can be declared in several different ways. It can be a class with a render() method. Alternatively, in simple cases, it can be defined as a function. In either case, it takes props as an input, and returns an element tree as the output. JSX transpiled as createElement at the end.

function Button ({ onLogin }) {
  return React.createElement(
    'div',
    {id: 'login-btn', onClick: onLogin},
    'Login'
  )
}