substring function in react js

import React from 'react';

function SubstringEXP(props) {

    var str = "Hello world, react js SubString example";

    return (

        <div>

            <div><h1>SubString example</h1></div>

            {str.substring(0,10)}

        </div>

    );

}

export default SubstringEXP;

Github link: https://github.com/adi501/react-js-example