Use WordPress as the headless CMS of your single-page application
The posts and the custom posts of your WP site are automatically available via REST API. For example, if you want to fetch your latest posts, send a request to http://yourdomain.com/wp-json/wp/v2/posts. Almost all data related to your contents is available via REST API. A detailed list of the routes can be found here.
If you are fetching data via REST API and want the contents to be unavailable on the main WordPress site to avoid duplicate contents, install this plugin. This plugin will make all other pages of your main WordPress site unavailable and leave only the WordPress dashboard and the REST API for use.