NodeJS is an open-source, cross-platform, back-end, JavaScript runtime environment that executes JavaScript code outside a web browser. NodeJS lets developers use JavaScript to write command line tools and for server-side scripting—running scripts server-side to produce dynamic web page content before the page is sent to the user's web browser. Consequently, NodeJS represents a "JavaScript everywhere" paradigm, unifying web-application development around a single programming language, rather than different languages for server-side and client-side scripts.