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

Answer

The two approaches are not interchangeable. You should initialize state in the constructor when using ES6 classes, and define the getInitialState method when using React.createClass.

class MyComponent extends React.Component {
constructor(props) {
super(props);
this.state = { /* initial state */ };
}
}
is equivalent to

var MyComponent = React.createClass({
getInitialState() {
return { /* initial state */ };
},
});