add Floki.find_by_id/2

[SteffenDE]

Related to the problem and discussion in phoenixframework/phoenix_live_view#3144.

In LiveViewTest we need to find elements by their id. Currently, we use Floki.find(html, "##{id}"), but this breaks as soon as there are special characters in the id. We could use Floki.find(html, %Floki.Selector{id: id}), but the Floki.Selector struct is not documented and therefore I'm not sure if it's something to rely on.

As document.getElementById is also a frequently used API in the browser, adding a find_by_id or similar function to Floki could be quite useful.

This PR adds a simple find_by_id function that internally uses the %Floki.Selector{id: id} struct.
As using find with a string is deprecated, I did not add this functionality to find_by_id.

[SteffenDE]

Maybe we should also only return nil or the first element found? That would mirror the behavior of document.getElementById. Not sure what Floki does when ids are not unique. We could also raise if there are multiple results.

[ypconstante]

I think returning the first element is the best option, in the future we could implement an optimization to stop the traversal on the first matching node, and has the same behaviour as getElementById.
The function could be called find_one_by_id or find_first_by_id to make it more explicit.

[philss]

Maybe we should also only return nil or the first element found?

@SteffenDE yeah, I agree. We don't need to return a list here.

The function could be called find_one_by_id or find_first_by_id to make it more explicit.

I believe if we document well, it's OK to use find_by_id. WDYT @josevalim ?

[philss]

Only minor points, but LGTM!

[josevalim]

What about calling it “get” to mirror browsers then? Or get_by_id?

[philss]

What about calling it “get” to mirror browsers then? Or get_by_id?

I like the idea of using get_by_id! WDYT @SteffenDE ?

[SteffenDE]

@philss yep, I like it too. Changed it.

[philss]

🚢

[philss]

@SteffenDE thank you for the contribution!

and thanks @ypconstante and @josevalim for the points and the discussion!