Once you test a URL, you can view the rendered HTML, page loading issues and a JavaScript console containing warnings and errors. And remember, this is the desktop render, not mobile.

The JavaScript is still working behind the scenes. Essentially, we get a more granular HTML syntax, which can just load segments instead of whole pages, and can submit Ajax requests.

Output: The results of executing the CSS, HTML, and JavaScript entered into the sections of the page. Figure A shows jsFiddle loaded in Internet Explorer 9 with empty code panes. Figure A ...

The HTML is parsed, JavaScript is executed, and the result is the DOM. The content of a web page is not (just) source code, it’s the DOM. This makes it pretty important.