JQuery Footguns?

One thing I just remembered:

I used to use a convention to distinguish jQuery objects from regular variables, stuff like var $textBox = $("#textBox"). Don't know if it still makese sense but it did at the time :D

Short list of things that come to mind:

• Take the time to compare the jQuery AJAX stuff to a minimal open-coded implementation covering exactly what you need. You'll often find that just coding it yourself will both save space (if you can use a custom build of jQuery with the AJAX stuff stripped out) and save time. It also makes migrating to jQuery alternatives a bit easier. The same goes for the animation stuff (by the way, if you need animations more powerful than the basic canned stuff jQuery provides, I'd suggest looking into Anime.js, it's fast, tiny, and very powerful).
• Cache your jQuery objects. For really trivial cases, performance isn't too bad, but the moment you start getting complex selectors (or using class selectors on older browsers), you will see some serious performance issues.
• Use .prop() instead of .attr() whenever you can. It's significantly more efficient, and it ensures that the browser's internal understanding of the DOM state gets updated properly. Even further, use specific jQuery methods for the properties that have them (value for example, which has the .val() method).
• Use event delegation whenever possible. This will help keep the number of event listeners down, which in turn helps a lot with app performance on many devices. Using event delegation also means you don't have to care if the specific element you want to match on even exists in the DOM when you add the event.
• Make sure to keep track of which variables refer to jQuery objects. Most people just prefix such variables with $ as a reminder. This is more a case of writing readable code than actual performance.
• Remember that jQuery always returns a valid object, even if your selector matches nothing (in that case, you get an empty jQuery object). This actually does have practical uses, but it also means that things that would crash if done through VanillaJS methods will silently fail to do what they say when using jQuery.
• Keep in mind that many jQuery methods apply to all matched elements. In a lot of cases, there's no point in manually looping over the returned results of a jQuery selector call because you can simply update everything with one function call (which will be faster, especially for very large numbers of matched nodes).
• Pretty much every jQuery method which mutates the state of the DOM returns the jQuery object it was called on. As such, you can often chain a series of methods that modify your selected element. While this doesn't make things any faster (at least, not measurably on any sane JS engine), it does make the JS code a bit smaller (each method you chain this way saves 2 bytes of code after running the source through a minifier).
• Certain jQuery methods (most notably .addClass() and .removeClass()) are functionally idempotent and declarative. Put simply, $('#foo').removeClass('bar') will never return an error, and will always ensure that the element with ID foo does not have the class bar. As a result, stuff like this just wastes time:

if (!$('#foo').hasClass('bar')) {
    $('#foo').removeClass('bar')
}

Also, you might want to see if you can convince the decision maker to use Cash instead, it's like jQuery, just significantly smaller and significantly faster (and it unfortunately doesn't work with Bootstrap or some popular jQuery plugins like select2).

Something that I learned from jQuery was the event delegation and is easy to implement:

$('#parent').on('click', '#dynamicCreatedChild', e => {})

A good thing to remember too is the data() method used in jQuery not set values in data attr but can read it.

Using the data() method to update data does not affect attributes in the DOM. To set a data-* attribute value, use attr

docs

And use a internal system of cache, so if you update the attr data you need to retrieve with attr().

Since jQuery 1.4.3, data-* attributes are used to initialize jQuery data. An element's data-* attributes are retrieved the first time the data() method is invoked upon it, and then are no longer accessed or mutated (all values are stored internally by jQuery).

docs

hey, non related question but are you a freelancer or a full-time worker?

Actually jQeury is not so bad. Especially the UI version of it its quite modular and you can build big applications with it. Just don't couple UI logic with business logic.

The module pattern should help: learn.jquery.com/code-organization...

Saw this yesterday, you may want to consider it over jQuery blissfuljs.com/

Haven't worked with it so far

Depending on the browsers the app is going to run, you may consider not use jquery at all: youmightnotneedjquery.com/

Thanks for this! Great point that you always get back a JQuery object - those extra null checks are clunky otherwise.