I was reading this article on using observables and came across several instances where the writer wrote something like this:

map((value: IObj) => {
  return value.name!.value; // << What is this??
})

I've never seen this exclamation point and dot combo before. The writer does this a few times in the article for me to think that it's a typo. I know about ?. but I've never seen !. in JS, TypeScript, or Flow.

Can someone help me understand what that is? Specifically:

• what is it called?
• Is it JS or TS?
• If JS, when was it introduced?
• Most importantly, what does it do?