看看官方的描述：
Description
jsFiddle is the playground for web developers, an online editor for web snippets. Helps to isolate bugs. Many frameworks supported.
jsFiddle is a playground for web developers, a tool which may be used in many ways. You can use it as an online editor for snippets build from HTML, CSS and JavaScript.
Share your Fiddle. Embedded on a blog, tweet URL to edit or result page. Using this approach, JavaScript developers can very easily isolate bugs.
Many actively developed frameworks are supported - it helps with testing backward compatibility of your plugins.
Your code may be shared from GitHub and displayed as new Fiddle.
Draft functionality provides an ability to test your Fiddle in many devices or browsers.
http://jsfiddle.net/
它包括了顶端的控制按钮，你可以执行Run，update，Fork，reset ，下面的4个windows你可以分别调试HTML，CSS，Javascript，在左边的操作区，你可以选择相关的js类库，支持的还是相当全的。当然，也支持自定义的类库，这个很不错。