Does the [removed] tag position in HTML affects performance of the webpage?

Question

If the script tag is above or below the body in a HTML page, does it matter for the performance of a website?

And what if used in between like this:

Answer 1

Yes, it does affect the performance of the web page.

The problem with JavaScript is that is blocks the execution/loading of the rest of the page. If you have something that takes a long time in your JavaScript then it will prevent the rest of the page from loading:

See these examples:

• Script at top, blocks whole page: http://jsfiddle.net/jonathon/wcQqn/
• Script in the middle, blocks bottom: http://jsfiddle.net/jonathon/wcQqn/1
• Script at bottom, blocks nothing: http://jsfiddle.net/jonathon/wcQqn/3/

You can see the effect the alert has on the rendering of the rest of the page. Any JavaScript that you put into the top of your page will have the same effect. In general, it is better to put anything critical to the layout of your page (i.e. menu plugins or something). Anything that requires a user interaction (popup handlers) or doesn't involve the user at all (Google Analytics) should go to the bottom of the page.

You can get lazy loaders that will inject your script tags into your code. Since the code isn't on the HTML, you can be sure that your whole page has rendered correctly and that the JS you're including will not block anything.