Xpath 开发速查表

Testing

Xpath test bed

Test queries in the Xpath test bed:

• Xpath test bed (whitebeam.org)

Browser console

$x("//div")

Works in Firefox and Chrome.

Selectors

Descendant selectors

Attribute selectors

Order selectors

Siblings

jQuery

Other things

Class check

//div[contains(concat(' ',normalize-space(@class),' '),' foobar ')]

Xpath doesn’t have the “check if part of space-separated list” operator, so this is the workaround (source).

Expressions

Steps and axes

Prefixes

Begin your expression with any of these.

Axes

Separate your steps with /. Use two (//) if you don’t want to select direct children.

Steps

//div
//div[@name='box']
//[@id='link']

A step may have an element name (div) and predicates ([...]). Both are optional. They can also be these other things:

//a/text()     #=> "Go home"
//a/@href      #=> "index.html"
//a/*          #=> All a's child elements

Predicates

Predicates

//div[true()]
//div[@class="head"]
//div[@class="head"][@id="top"]

Restricts a nodeset only if some condition is true. They can be chained.

Operators

# Comparison
//a[@id = "xyz"]
//a[@id != "xyz"]
//a[@price > 25]

# Logic (and/or)
//div[@id="head" and position()=2]
//div[(x and y) or not(z)]

Use comparison and logic operators to make conditionals.

Using nodes

# Use them inside functions
//ul[count(li) > 2]
//ul[count(li[@class='hide']) > 0]

# This returns `<ul>` that has a `<li>` child
//ul[li]

You can use nodes inside predicates.

Indexing

//a[1]                  # first <a>
//a[last()]             # last <a>
//ol/li[2]              # second <li>
//ol/li[position()=2]   # same as above
//ol/li[position()>1]   # :not(:first-child)

Use [] with a number, or last() or position().

Chaining order

a[1][@href='/']
a[@href='/'][1]

Order is significant, these two are different.

Nesting predicates

//section[.//h1[@id='hi']]

This returns <section> if it has an <h1> descendant with id='hi'.

Functions

Node functions

name()                     # //[starts-with(name(), 'h')]
text()                     # //button[text()="Submit"]
                           # //button/text()
lang(str)
namespace-uri()

count()                    # //table[count(tr)=1]
position()                 # //ol/li[position()=2]

Boolean functions

not(expr)                  # button[not(starts-with(text(),"Submit"))]

String functions

contains()                 # font[contains(@class,"head")]
starts-with()              # font[starts-with(@class,"head")]
ends-with()                # font[ends-with(@class,"head")]

concat(x,y)
substring(str, start, len)
substring-before("01/02", "/")  #=> 01
substring-after("01/02", "/")   #=> 02
translate()
normalize-space()
string-length()

Type conversion

string()
number()
boolean()

Axes

Using axes

//ul/li                       # ul > li
//ul/child::li                # ul > li (same)
//ul/following-sibling::li    # ul ~ li
//ul/descendant-or-self::li   # ul li
//ul/ancestor-or-self::li     # $('ul').closest('li')

Steps of an expression are separated by /, usually used to pick child nodes. That’s not always true: you can specify a different “axis” with ::.

Child axis

# both the same
//ul/li/a
//child::ul/child::li/child::a

child:: is the default axis. This makes //a/b/c work.

# both the same
# this works because `child::li` is truthy, so the predicate succeeds
//ul[li]
//ul[child::li]

# both the same
//ul[count(li) > 2]
//ul[count(child::li) > 2]

Descendant-or-self axis

# both the same
//div//h4
//div/descendant-or-self::h4

// is short for the descendant-or-self:: axis.

# both the same
//ul//[last()]
//ul/descendant-or-self::[last()]

Other axes

There are other axes you can use.

Unions

//a | //span

Use | to join two expressions.

More examples

Examples

//*                 # all elements
count(//*)          # count all elements
(//h1)[1]/text()    # text of the first h1 heading
//li[span]          # find a <li> with an <span> inside it
                    # ...expands to //li[child::span]
//ul/li/..          # use .. to select a parent

Find a parent

//section[h1[@id='section-name']]

Finds a <section> that directly contains h1#section-name

//section[//h1[@id='section-name']]

Finds a <section> that contains h1#section-name. (Same as above, but uses descendant-or-self instead of child)

Closest

./ancestor-or-self::[@class="box"]

Works like jQuery’s $().closest('.box').

Attributes

//item[@price > 2*@discount]

Finds <item> and check its attributes

References

• Xpath test bed (whitebeam.org)