[Moving to wikitech-l; mediawiki-l is a little off-topic.]
On Mon, 26 Jul 2021 at 21:27, Yaron Koren <yaron57(a)gmail.com> wrote:
Hi,
I've been trying to get rid of the ESLint warnings for the JavaScript code
in some of my extensions, when they go through Jenkins validation. One
warning that appears fairly often is this one:
Where possible, maintain application state in JS to avoid slower DOM
queries
no-jquery/no-class-state
I'm not sure if this is a warning that's specific to Wikimedia code, but
doing a web search on it brings up this Wikimedia help page as the only
real result:
https://github.com/wikimedia/eslint-plugin-no-jquery/blob/master/docs/rules…
Yes, we forked the dead "jquery" upstream eslint plugin and have expanded
it significantly. In general, the plugin's purpose
<https://www.npmjs.com/package/eslint-plugin-no-jquery> is to discourage
use of jQuery functions, especially where the functions are deprecated or
have faster native equivalents. (Almost all uses of jQuery are no longer
necessary given that the vast majority of the Web only runs on
modern-enough browsers.)
This page is rather confusing. It says that the warning comes when calling
either hasClass() or toggleClass() on a jQuery
element. That part makes
sense, but then the suggested alternatives are strange. The page says that
the following are some examples of bad code:
$( 'div' ).hasClass();
$div.hasClass();
In their place, it suggests the following:
hasClass();
[].hasClass();
div.hasClass();
No, it doesn't. It says that our code is clever enough to not think that
these false positives are issues that you need to fix. It's not saying you
should use a method called hasClass(); it's saying that you should maintain
state inside JS; this is principally a performance/code smell test.
If your code is triggered from a non-JS DOM (e.g. painted from PHP), the
first time you grab state from the DOM is unavoidable (and so you'd use an
inline disable), but thereafter you should keep track of such details in
JS. An example of this is in the initialisation code for Notifications
("Echo"), where it has to grab the state from the DOM
<https://gerrit.wikimedia.org/g/mediawiki/extensions/Echo/+/HEAD/modules/ext.echo.init.js#46>
for a couple of items, but does so only once.
Sorry that this is confusing! We could put together a narrow JS tips and
tricks page and link to that from the linter, but most of these have been
fixed over the years since we introduced this in Wikimedia production code
so there's not been much call.
J.
--
*James D. Forrester* (he/him <http://pronoun.is/he> or they/themself
<http://pronoun.is/they/.../themself>)
Wikimedia Foundation <https://wikimediafoundation.org/>