It is an attribute which helps to store a reference to a particular React element or component returned by render(). They come in handy when we need DOM measurements or to add methods to the components.
class ReferenceDemo extends React.Component{
display() {
const name = this.inputDemo.value;
document.getElementById('disp').innerHTML = name;
}
render() {
return(
<div>
Name: <input type="text" ref={input => this.inputDemo = input} />
<button name="Click" onClick={this.display}>Click</button>
<h2>Hello <span id="disp"></span> !!!</h2>
</div>
);
}
}