"Days since 2000" Scratch block should have a Leopard util

[towerofnix]

Right now sb-edit converts sensing_dayssince2000 into this:

(((new Date().getTime() - new Date(2000, 0, 1)) / 1000 / 60 + new Date().getTimezoneOffset()) / 60 / 24)

In principle, this seems sound: "days since 2000" is a slightly ridiculous block and exposing users to real-world JavaScript date manipulation is basically a good idea.

The issue is, Scratchers aren't trying to figure out Date Mathematics when they use this block — and Scratch has blocks for date math. ("current minute", "current second", etc.) By replacing a simple Scratch block with much more complexity in JavaScript, we're only introducing overhead.

There exist a number of other functions (most recently compare & friends, as well as scratchTan) which ensure compatibility with Scratch without bringing obtuse or overly-explicit syntax to generated projects. I think the behavior for "days since 2000" should be moved into one of these. Let's call it... this.daysSince2000()! 👻

[towerofnix]

Just to make a case against such a function as this.daysSince(new Date(2000, 0, 1)): IMO if we add a generic function, we're 1) opening up to arbitrarily going further than Scratch [with the standard library], which isn't a design goal of Leopard, and 2) limiting incentive to learn how that function works yourself, as a user, and come up with an alternative which suits your case more specifically.

We don't expose Leopard's inner workings to users right now, but overall, I think if we want to more specifically introduce users to JavaScript programming concepts, there are a number of better ways than by replacing a very compact standard utility with a bunch of "magic words" users will likely just copy and paste, gloss over, or be flat-out overwhelmed by.

[towerofnix]

If we want to simulate re-running a project deterministically [not generally but for the purpose of testing and catching behavior changes], we need to be able to mock this block anyway, which we basically can't do when directly accessing Date behavior.