JavaScript is a general purpose scripting language commonly used as a client side language inside of a web browser. Originally released in 1995 in Netscape Navigator, JavaScript was designed to allow some level of automation on a displayed web page, something that was only available through the Java programming language at the time. JavaScript, despite its name, has nothing to do with Sun's Java programming language.
JavaScript is used on the display side of any web site we create to add interactivity and validation to each page. You can use JavaScript with any other back-end web technology.