Attributes of elements

html_attr() reads one attribute from every node; html_attrs() reads all of them; html_classes() splits the class attribute into tokens. Values are decoded (& becomes &). An attribute that is present but empty is "", distinct from an absent one: test a boolean attribute such as disabled by presence, !is.na(html_attr(x, "disabled")).

Usage

html_attr(x, name, default = NA_character_)

html_attrs(x)

html_classes(x)

Arguments

x

A zuhtml_document or zuhtml_nodeset.

name

The attribute name: a single string.

default

The value for nodes that lack the attribute, including nodes that are not elements: a single string, possibly NA.

Value

• html_attr(): a character vector as long as x; NA for missing nodes.

• html_attrs(): a list as long as x of named character vectors, in source order; NA_character_ for missing nodes.

• html_classes(): a list as long as x of character vectors of class tokens; NA_character_ for missing nodes.

Details

Attribute names on HTML elements match regardless of ASCII case, as in a browser; on SVG and MathML elements they match exactly (viewBox). Namespaced attributes in foreign content are named with their prefix, as in "xlink:href". Where an element has the same attribute more than once, the first wins, as the HTML parser decides.

See also

Other node values: html_markdown(), html_name(), html_serialize(), html_strings(), html_text(), html_text_clean()

Examples

doc <- html_parse(
  "<a href='/x' class='btn  primary' data-id=7>Go</a><input disabled>"
)
body <- html_children(html_root(doc))[2]
nodes <- html_children(body)
html_attr(nodes, "href")
#> [1] "/x" NA  
html_attr(nodes, "href", default = "")
#> [1] "/x" ""  
html_attrs(nodes)
#> [[1]]
#>           href          class        data-id 
#>           "/x" "btn  primary"            "7" 
#> 
#> [[2]]
#> disabled 
#>       "" 
#> 
html_classes(nodes)
#> [[1]]
#> [1] "btn"     "primary"
#> 
#> [[2]]
#> character(0)
#> 
!is.na(html_attr(nodes, "disabled"))
#> [1] FALSE  TRUE