Node.js allows the creation of Web servers and networking tools using JavaScript and a collection of "modules" that handle various core functionalities.[29][32][46][47][48] Modules are provided for file system I/O, networking (DNS, HTTP, TCP, TLS/SSL, or UDP), binary data (buffers), cryptography functions, data streams, and other core functions.[32][47][49] Node.js's modules use an API designed to reduce the complexity of writing server applications.[32][47] JavaScript is the only language that Node.js supports natively, but many compile-to-JS languages are available.[50] As a result, Node.js applications can be written in CoffeeScript,[51] Dart, TypeScript, ClojureScript and others. Node.js is primarily used to build network programs such as Web servers.[46] The most significant difference between Node.js and PHP is that most functions in PHP block until completion (commands execute only after previous commands finish), while Node.js functions are non-blocking (commands execute concurrently or even in parallel,[52][53] and use callbacks to signal completion or failure).[