jsFiddle is the perfect solution; it provides a custom environment (based on user selections) to test (or fiddle with) your JavaScript, HTML, and CSS code ... the page is the menu area where ...

HTML form items like drop-down menus enable you to add dynamic functionality to your Web pages using JavaScript. Use the "Select" form to create your drop-down menu and include the list of website ...

We can also add drop-down menus to our HTML forms. We can use the select element to implement these drop-down menus. Input choices are in “option” elements as shown in the example below.