Expose they key data on a page within a JavaScript API.
More and more web applications and plugins these days are pure JavaScript, working in the browser without any kind of server-side communication.
What this means however, is that by default, they don't have the data they require available for them to use. This library makes that happen.
The library gets all the key information about a page from your Wordpress database and returns it in a JSON encoded format. This data can then be set as whatever global you wish within your theme/plugin.