Is jQuery still the go-to JS helper library?

JavaScript itself provides the functionality jQuery became popular for. So no. Check the standard lib first before considering helper libs.

It depends what you want to do and the amount of polyfills/backwards compatibility you need.

Nowadays most projects use one of the big frameworks like React/Vue/Svelte and others which take a vastly different approach to maintaining the DOM and for the most part you never manipulate nodes yourself, therefore you don't need jQuery and it's not used much anymore. JSX is weird at first but it's actually quite nice. Some of those libraries like SolidJS have impressively low overhead.

And for those that like to stick to just minimal JS, the browser APIs have matured a lot so a lot of jQuery isn't really necessary anymore either. We have querySelectorAll and things like Array.prototype.forEach and Array.prototype.map and arrow functions that cut down a lot on what shortcuts jQuery would offer. Visual effects are usually done with CSS animations and just switching up classes. Everything AJAX is easier and cleaner with the new fetch() function and accessories. Vanilla JavaScript is for the most part quite usable and easy these days. You can even create custom HTML elements from JavaScript to make your life easier!

But if you're looking at the jQuery API specifically, you can still use jQuery today. It's still maintained and functional. I think modern versions are pretty small too since it no longer needs half of it to be Internet Explorer hacks and other obsolete browsers that were holding web development back.

I 90% just want easy JSON POST.
- Yep, that's definitely covered: https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch#supplying_request_options
  
  If you end up using a bundler and npm dependencies, axios is also pretty good and very popular HTTP client.
JSX is fucking weird compared to vue
- Custom template language and custom DOM attributes are way weirder than just using language-native constructs (ternary operator, map/filter, variables, functions, etc.) directly like you can in JSX.
- Both are weird compared to Svelte.
- Vue sucks. A pretty graphic of a CGI robot convincing untrained programmers to merge their web files and produce unreadable garbage as the output file.

Hasn’t JS6 got most of what jQuery offers?

Yeah personally I haven't needed jQuery in years.
- Same here, tbh I haven't thought about jquery in a while and kinda came in here to see if it's dead or not. Yeah frameworks have largely eliminated the "need" for jquery libraries for most projects. It's weird to think about, didn't take too long to happen.
Except for animations and a few things.
- What do you mean about animations?
  
  Every use-case I can think about is already well supported by vanilla css/js without libraries or frameworks. (not including really out-there use-cases like game engines or image editors)
  
  Can you give an example?

A lot of jQuery's features are now available in native JS - would also suggest just using native JS anyway because jQuery won't throw any errors into the console if a selector matches no elements etc.

The only additional library I've needed recently for (personal work) is Axios for requests - easier than working with the Fetch API in some cases

Axios for requests - easier than working with the Fetch API in some cases

May I ask what cases? I used to use Axios on Node, before they implemented the fetch API over there but I haven't touched it since. And defintiely never used it on the client. Could you make an example of some case where it'd be easier to work with Axios than with fetch?
- For me it's the ability to set up a shared instance with the base request URL, and set headers for things like the user's token, allowing all requests made with that shared Axios instance to be sent to the right path with the token without needing to define them for each individual request.
  
  To be honest though something similar can be done with spread syntax in the Fetch API's options parameter

No, because the current practices have shifted from writing html+css+js in the classic style to using JavaScript frontend frameworks like vue, react, angular, svelte... Which offer a lot of features that would jQyery give you but also removed the need for some of them.
The paradigm has shifted and I don't think jQuery is used anymore (atleast not for new projects).

To explain this a bit further, the main difference between older jQuery-based projects and newer (React|Vue|Angular|Svelte)-based projects is imperative vs. declarative programming.

It used to be that you give commands (e.g. "when the user clicks this button, change that label content and add CSS classes to these elements"). Very quick to add something small, but also hard to grow and maintain well. It's easy to forget a command in some code paths.

Nowadays you declare state, and define how your UI is derived from that. This means you don't give commands to change things, instead you change data and your UI is updated automatically. This makes it much easier to understand a component, and allows for maintainable growth.

Jquery is a swear word in professional front end contexts, the replacement is transpilation and dropping ie support.

Personally I used jquery up until react and babel got hot, now I never touch the dom directly with jquery and no longer have a need for the polyfill features as I rely on babel preset-env to support the browsers we have selected (especially for things like promises/async await/es6+ features)

What do you still need babel for?

The only features that come to mind for anyone who needs to reach out to babel today would be those working on the tc39 proposals themselves.

IIRC most stuff can be done with vanilla JS in any modern browser.
Although, I've been doing little front-end work, and mostly for personal projects, nothing fancy nor production ready, so someone might have another opinion about using jQuery.

As mentioned, JavaScript may have everything you need. Check out https://youmightnotneedjquery.com/

Nowadays people use HTMX

Not sure why downvoted. HTMX does seem to be becoming popular. I prefer the simplicity of it.
- Because it's only gaining traction, while the commenter made it sound like everyone was using it instead of jQuery. Which is simply not true, everyone is using Vue, React, Angular, Svelte and so on.
Htmx for server requests and AplineJS for client interactions
Is it foss?