The callback function can handle requests with non-blocking I/O calls, and if necessary can spawn threads from a pool to execute blocking or CPU-intensive operations and to load-balance across CPU cores.
Node’s approach to scaling with callback functions requires less memory to handle more connections than most competitive architectures that scale with threads, including Apache HTTP Server, the various Java application servers, IIS and ASP.NET, and Ruby on Rails.
Also note that Node applications aren’t limited to pure JavaScript.
Node.js incorporates the Google Chrome V8 JavaScript engine, which supports ECMAScript 2015 (ES6) syntax without any need for an ES6-to-ES5 transpiler such as Babel.
In 1995 Brendan Eich, then a contractor to Netscape, created the JavaScript language to run in Web browsers?—?in 10 days, as the story goes.
The name JavaScript was chosen for marketing purposes, as Sun’s Java language was widely hyped at the time.