Node.js is an open-source, cross platform JavaScript run-time environment that executes JavaScript code outside of a browser. Typically, JavaScript is used primarily for client-side scripting, in which scripts written in JavaScript are embedded in a webpage's HTML and run client-side by a JavaScript engine in the user's web browser. Node.js lets developers use JavaScript to write Command Line tools and for client-side scripting, —running scripts server-side to produce dynamic web page content before the page is sent to the user's web browser.