Question

What is supposed to happen if I run jQuery’s load() function by supplying a page fragment that does not exist? Does it simply load the whole page, or does it load an empty page?

$("#a").load("http://www.example.com #non-existing-id");

Answer 1

From http://api.jquery.com/load/ (at section Loading Page Fragments)

We could modify the example above to use only part of the document
that is fetched:

$(‘#result’).load(‘ajax/test.html #container’);

When this method executes, it retrieves the content of ajax/test.html,
but then jQuery parses the returned document to find the element with
an ID of container. This element, along with its contents, is inserted
into the element with an ID of result, and the rest of the retrieved
document is discarded.

Since the element does not exist, nothing gets loaded within #a. However, please note that the whole page is still fetched from server.