How do I add an active class to a Link from React Router?

On the Link component you can now add activeClassName or set activeStyle.

These allow you to easily add styles to the currently active link.

Previously, you could create a custom component that works like a wrapper to Link with the following logic.

In a file called nav_link.js

import React from 'react';
import { Link } from 'react-router-dom';
import PropTypes from 'prop-types';

class NavLink extends React.Component {
    render() {
        var isActive = this.context.router.route.location.pathname === this.props.to;
        var className = isActive ? 'active' : '';

        return(
            <Link className={className} {...this.props}>
                {this.props.children}
            </Link>
        );
    }
}

NavLink.contextTypes = {
    router: PropTypes.object
};

export default NavLink;

And use it as given below in your component:

...
import NavLink from "./nav_link";
.....

<nav>
    <ul className="nav nav-pills pull-right">
        <NavLink to="https://stackoverflow.com/">
            <i className="glyphicon glyphicon-home"></i> <span>Home</span>
        </NavLink>
        <NavLink to="about">
            <i className="glyphicon glyphicon-camera"></i> <span>About</span>
        </NavLink>
    </ul>
</nav>