Selecting a css class with xpath

I want to write the canonical answer to this question because the answer above has a problem.

Our problem

The CSS selector:

.foo

will select any element that has the class foo.

How do you do this in XPath?

Although XPath is more powerful than CSS, XPath doesn't have a native equivalent of a CSS class selector. However, there is a solution.

The right way to do it

The equivalent selector in XPath is:

//*[contains(concat(" ", normalize-space(@class), " "), " foo ")]

The function normalize-space strips leading and trailing whitespace (and also replaces sequences of whitespace characters by a single space).

(In a more general sense) this is also the equivalent of the CSS selector:

*[class~="foo"]

which will match any element whose class attribute value is a list of whitespace-separated values, one of which is exactly equal to foo.

A couple of obvious, but wrong ways to do it

The XPath selector:

//*[@class="foo"]

doesn't work! because it won't match an element that has more than one class, for example

<div class="foo bar">

It also won't match if there is any extra whitespace around the class name:

<div class="  foo ">

The 'improved' XPath selector

//*[contains(@class, "foo")]

doesn't work either! because it wrongly matches elements with the class foobar, for example

<div class="foobar">

Credit goes to this fella, who was the earliest published solution to this problem that I found on the web:http://dubinko.info/blog/2007/10/01/simple-parsing-of-space-seprated-attributes-in-xpathxslt/

//[@class="date"] is not a valid xpath.

Try //*[@class="date"], or if you know it is an image, //img[@class="date"]

XPath 3.1 introduces a function contains-token and thus finally solves this ‘officially’. It is designed to support classes.

Example:

//*[contains-token(@class, "foo")]

This function makes sure that white space (not only (U+0020)) is handled correctly, works in case of class name repetition, and generally covers the edge cases.

Note: As of today (2016-12-13) XPath 3.1 has status of Candidate Recommendation.