Ask HN: Getting started with JavaScript app development

I've been advised by a prospective employer that local demand where I live (Finland) is exceedingly high, to the extent that I was told just expressing interest in learning mobile dev, especially in JavaScript, increased the chances of employing.

However, being willing to learn, and having at least some basic skills, are a doable step away, and I'd like to get my hands dirty and at least try maybe building a basic proof-of-concept app just to show I can do it.

Unfortunately finding actual "getting started" information that isn't aimed at existing developers, esp. for JS app dev, seems to be more difficult than I expected.

Would deeply appreciate any links, docs, etc.