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The new WordPress.com codebase, codenamed "Calypso," moves WordPress.com away from MySQL and PHP. It's built entirely in JavaScript, and communicates with WordPress.com only using our REST API. This means the new WordPress.com is a browser-based client for our API, just like any other application built on top of it — lighter, faster, and more flexible for a mobile-focused world.

Calypso uses a thin layer of Node.js on the server to build the initial web page, and much of the logic is run in the client as a Single Page Application (SPA) built in-house, leveraging many other open source JavaScript modules. Calypso adopted Facebook's React view library early on, and has been heavily influenced by other open source work in the React community.
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