空的SRC属性和较差的性能

Question

Recently I read this article by Nicholas C. Zakas:

http://www.nczonline.net/blog/2009/11/30/empty-image-src-can-destroy-your-site/

It says that empty SRC attributes in IMG and SCRIPT files for example can cause poor performance. My question is:

Are there still the same performance issues if there is NO src attribute at all?

Example:

<img id="image" />

Also, how will the browser interpret this? Would the above code be problematic anywhere?

Much obliged for any help.

Answer 1

This is from a very old version of the HTML spec :

SRC (Source)

The SRC attribute specifies the URI for the image to be embedded. Its syntax is the same as that of the HREF attribute of the tag. SRC is mandatory.

@src is required, so if you have an <img> with missing @src , then it wouldn't be a valid HTML. Browsers are very tolerant though, but what they will do in this situation is probably implementation specific.

EDIT: from HTML 5 spec :

The src attribute must be present , and must contain a valid non-empty URL potentially surrounded by spaces referencing a non-interactive, optionally animated, image resource that is neither paged nor scripted.

So, an <img> with missing or empty @src would not be valid HTML.

AFAIK, HTML 5 still does not specify how browsers should handle missing src attribute, although it did say:

If the src attribute is not set and either the alt attribute is set to the empty string or the alt attribute is not set at all

The element represents nothing.