The "use strict" thing is interesting. I often hear people say, well we can't fix absurd behavior in JS because backwards compatibility! Well, we already did, and we can do it again!
Brilliant. I have a similar idea for a language I've been envisioning.
So, my approach to dynamic features, global mutable state, etc... There's this big list of features which have caused me tremendous pain over the years. I am increasingly weary.
Sometimes you want or need them, though. You don't want the same level of strictness for every project (e.g. throwaway scripts or game jams), nor at every stage of a project -- e.g. being forced to specify invariants is something I'd love to be able to enable, but I wouldn't want that on while I'm still figuring out the basic structure of things.
So for game jams I'd put the language into #JAMMODE (which would be short for a bunch of other flags). But the point here is that jam mode should be opt-in, rather than opt-out. You should have to go out of your way to enable the footguns. And a file with #JAMMODE should be a little smelly. You should think, OK I'm actually shipping this thing now, let's get it out of #JAMMODE. (And strict files can't talk to jam files, and we probably want different strictness levels beyond Debug and Release, etc... someone told me with the strictness "zones" that I'm reinventing half of Ada, hahah.)
I became hopeful for a moment, then saw it's from 2015. Ouch! (Also, I love the name. I had a similar idea I called "use sane", but obviously that one wouldn't have gotten far...)
The strong typing thing is really interesting. After using JavaScript for a while, I developed PTSD around dynamic types. I became convinced that static typing was the only way to avoid hell.
Then I used Python for a while, and... experienced approximately none of my previous pain. I found that quite odd. Turns out what I was actually after was a sane type system, not a static one. In other words, strong types rather than weak ones.
I do think there are additional benefits to static typing, especially for larger projects and serious work. But I was surprised that most of the pain-delta was in this first jump: