YSlow: Avoid empty src or href
Empty src or href attributes can cause multiple problems.
How does your site score on this recommendation?
You might expect a browser to do nothing when it encounters an element with an empty src or href attribute, however this is not the case in a considerable number of browsers. As of 2016, IE and Edge will both make a request to the page’s parent directory, while Firefox and older Webkit browsers (like Safari) will re-request the page itself! This behavior could potentially corrupt user data, waste server computing cycles generating a page that is never viewed, or in the worst case, cripple your servers by sending them a large amount of unexpected traffic.
Problem Element–Attribute Pairs in Modern Browsers
According to our research, these three pairs will cause needless requests in IE 10+ & all versions of Edge:
<html manifest=""> <embed src=""> <object data="">
Likewise, these two appear to affect all versions of Firefox:
<video poster=""> <script src="">
Additional Problem Pairs in Older Browsers
While their later versions aren’t affected, Safari < 5.1, IE < 9, iOS < 6, and Android < 4.4 all make needless requests in the presence of many of these element–attribute pairs:
<link rel="stylesheet" href=""> <img src=""> <input type="image" src=""> <audio src=""> <video src=""> <source src="">