1859297 - Add lint rule to stop using .tagName as its case depends on XHTML/HTML-ness of the document, source casing, and element's namespace prefix

Status: NEW

(Developer Infrastructure :: Lint and Formatting, enhancement)

Description

[:Gijs (he/him)]

There are a few different problems with .tagName:

• its case differs for the same source code depending on whether it's used in an HTML or XHTML document (in HTML, it's always upper case, in XHTML, source case)
• changing the source case changes the case of tagName in XHTML documents (so other lint changes that e.g. enforce lowercasing tag names in the source markup can break JS checks using .tagName)
• it includes the namespace prefix if present in the XML case. So <html:input> and <input> where the parent sets the namespace for children produce a different tagName value, even though both are HTML Input elements

The combination of these problems is going to bite us if we switch some of our XHTML docs to HTML, as existing checks will start failing because the value of tagName will change, even though the markup won't.

We should probably just encourage people to use localName combined with a namespaceURI check if the namespace matters (it often doesn't).

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The severity field is not set for this bug.
:andi, could you have a look please?

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