JavaScript only works inside another application, the web browser. Whether that's IE or Safari or Firefox or Chrome or Opera, they all have a JavaScript engine inside them. The operating system runs the web browser, the web browser contains a page, and the page contains the JavaScript. Now another way JavaScript is limited is that yes, it doesn't have access to the file system of the computer that it's running on. There are no words in JavaScript to open or save local files because that would be a security risk.