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.