my_react_theme/functions.php

<?php
// This file is put in wp-content/themes/my_react_theme/

function my_theme_setup() {
    // Add support for automatic <title> tag.
    add_theme_support( 'title-tag' );
}
add_action( 'after_setup_theme', 'my_theme_setup' );

function my_theme_scripts() {
    // Enqueue the Backbone JavaScript Client.
    wp_enqueue_script( 'wp-api' );
}
add_action( 'wp_enqueue_scripts', 'my_theme_scripts' );