Files containing the JS extension are most commonly associated with JavaScript files. They contain JavaScript code used to execute instructions in a webpage that uses client-side scripting. Its functions may include the validation of form fields, rollover images, drop-down menu creation and other functions. These functionalities may also include automatically closing or opening Web browser windows or tabs and mouseovers. These JavaScript codes can also be used to create dropdown boxes with interactive functionalities. The JS file also contains all the HTML HEAD and BODY objects in the tags of the HTML page. Microsoft Notepad can be used to open and view the content of these .JS files. The JS file extension is also used for JACOsub script files, JetScript output files, Netscape settings files and ECMAScript language files. At times the JS files may become infected by a virus or trojan and should be carefully scanned if you receive a JS from someone sends in an email. Looking for how to open js files? Checkout http://www.openthefile.net/extension/js