Re: elisps dom library doesn't work as I expect

[Tim Landscheidt <tim@tim-landscheidt.de>]

Stefan Huchler <stefan.huchler@mail.de> wrote:

>> dom-by-tag returns a list of DOM elements; however,
>> dom-elements expects a single DOM element as its second ar-
>> gument.  So you need to iterate over the list of DOM ele-
>> ments returned by dom-by-tag and call dom-elements on each,
>> or use dom-search, etc.

> Interesting, I find the documention of dom-elements confusing:
>> Find elements matching MATCH
> what are the "elements" then? attributes not tags/ dom entries? But yes
> that would be a bugreport about the documentation also that dom-elements
> is not even listed in the gnu doku seem strange to me.

"Elements" in the context of dom-elements means the children
of the node passed as DOM (AFAICT).

> But maybe I am just not good enough in xml lingo.

That's not really a problem here as it is not /the/ prob-
lem :-); the dom-* functions only lightly relate to XML or
DOM concepts in JavaScript & Co. so one has to refer to the
Emacs "model".  As almost everything is a list in Emacs, one
does not get a meaningful error when using the DOM functions
incorrectly but instead the code just does not work.

> Could you explain a bit or show a example of the dom-search function or
> explain it's parameters. I have no idea what in the docstring
> "predicate" means and in what format it's expected, is Predicate a known
> term for something specific?

A predicate in Emacs Lisp is typically a (possibly
anonymous) function that looks at something and then returns
t for some values and nil for others.  So for your use case,
you could write something à la:

| (let
|     ((dom (with-temp-buffer (url-insert-file-contents
|                              "https://www.ebay.com/itm/185887279856")
|                             (libxml-parse-html-region (point-min) (point-max)))))
|   (dom-attr (car
|              (dom-search
|               dom
|               (lambda (d)
|                 (and (equal (dom-tag d) 'meta)
|                      (equal (dom-attr d 'itemprop) "name")))))
|             'content))

This will iterate over all DOM elements in the document,
return those that have a tag "meta" and an attribute
"itemprop" with the value "name", take the first (and
probably only) one, and return the value of this element's
"content" attribute.

Tim