What is the difference between using constructor vs getInitialState in React / React Native?

Answer

The difference between constructor and getInitialState is the difference between ES6 and ES5 itself.
getInitialState is used with React.createClass and
constructor is used with React.Component.

Hence the question boils down to advantages/disadvantages of using ES6 or ES5.

Let's look at the difference in code

ES5

var TodoApp = React.createClass({
propTypes: {
title: PropTypes.string.isRequired
},
getInitialState () {
return {
items: []
};
}
});

ES6

class TodoApp extends React.Component {
constructor () {
super()
this.state = {
items: []
}
}
};