The programming environment usually is not deployed to the runtime environment, so it's not a part of the built program. Libraries are.
"Vanilla" language or tool has a precise meaning of using the official tool without external customizations. If you are importing a library that is not part of the language standard specification, that's by definition not vanilla.
Using a development environment is not a "customization" of the language, because javascript has no official development environment that you could customize by using a different one, so the environment is not a part of the language.
For languages like Smalltalk implementations that have an IDE+runtime that is THE official development environment and specification, switching the code to a different IDE+runtime would indeed be using a non-vanilla version.
index.js
var foo = document.body.getElementById("bar");
That is dom manipulation using vanilla javascript in all modern browsers. I can use webpack, rollup, parcel, or load it in a script tag, it doesn't matter it's still just plain old javascript.
true, it doesn't. but imo when people say "vanilla js" they mean both no framework to abstract DOM manipulation and no build steps, whether they be transpiling from ES7 or bundling stuff. perhaps webpack can be used to just minify+concatenate a few files together, but that's not how it's usually used, and i guess not what most people mean when they talk about webpack.
i am a bit biased, based on my recent experience of trying to load a webpacked library's `dist/foobar.js` into a WordPress thing via a normal <script src="..."> and having it barf all over the console, yelling about `window.module` missing and loaders and stuff. i never managed to get the bundled version to load, which reinforces my opinion - it's not "vanilla" if it needs some custom infrastructure and can't just be dropped into an existing plain js environment.
i did however manage to load the unbundled source with a native ES6 <script type="module">, and it worked great! vanilla js can be pretty pleasant these days :)
i'm sure it means many things to many people :) obv i only speak myself here
ignoring framework stuff (bc everyone seems to agree there) i'd say if your js qualifies as "vanilla" if it can run in a relatively recent browser without a build step or other transformations. you might further ES5-ify, uglify and minify it for practical reasons, but that must be an optional thing
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since we're splitting hairs, we could also distinguish "theoretically vanilla js" - js that's standard ECMAScript so it'll run fine when browser catch up, but it's not supported just yet and thus needs transforming. this would exclude non-standard extensions like JSX
and note that i don't mean "vanilla" as any sort of value judgement! it's a practical description of how it works, not some kind of platonic ideal to aspire to – frameworks, webpack, Babel etc provide useful solutions for the shortcomings of the browser platform and ecosystem. the thing i was talking about is a single-file internal tool, and compat isn't a problem; if it was user-facing, i'd probably use some ES5-ifying tool myself. and i'd probably use JSX if i was doing a React thing, because it's great - inline HTML is an underappreciated convenience in PHP!