JavaScript is a light-weight programing language that is commonly used in web applications to allow client-side scripts to interact with the user to make the web application more dynamic, but can also be used outside the web environment.  The client-side nature of JavaScript means that logic and behavior can be performed locally on the user’s browser rather than traveling back to the web server.  This speeds up the responsiveness of the application and allows for a more seamless interaction with the user. All modern applications use JavaScript and may use a JavaScript framework or library to simplify and standardize client-side development for a web application, such as JQuery.