Add es3.d.ts

[Kagami Sascha Rosylight (saschanaz)]

Revives #16077

Fixes#2410
Fixes#15978

Intentionally included only NaN in es3.d.ts to initially generate minimal baseline changes.

[Eric Robinson (ericdrobinson)]

Am I missing something or is the current setup one that would have an es3.d.ts-only project have nothing beyond NaN defined? Shouldn't the es3.d.ts file contain most of what's included in the current es5.d.ts?

Unless I'm missing something, the current es3.d.ts looks... pretty useless, no?

[Kagami Sascha Rosylight (saschanaz)]

Eric Robinson (@ericdrobinson) The OP says:

Intentionally included only NaN in es3.d.ts to initially generate minimal baseline changes.

Moving all in once is doable but generates tons of baseline changes, which will make this PR hard to review. I want to get some review about code changes first and then move remaining types.

[Ryan Cavanaugh (RyanCavanaugh)]

In the intervening years since #2410 was logged, pretty much all the ES3 targets have died out (even the use cases identified most recently don't even really count as a true ES3 target).

Something we should have realized four years ago was that this would be a breaking change! Anyone targeting ES3 but using ES5 APIs (which is an entirely reasonable state to find yourself in if your actual runtime is ES5 and you're not using getters/setters, or if you're using polyfills) is going to be broken if we merge this and make target: ES3 align to lib: ES3.

So given the relative lack of remaining use cases for this, and the fact that to preserve back compat we'd have to make this an opt-in that you can effectively already achieve today with noLib, we're going to have to pass on this. Sorry for not identifying that problem earlier - we definitely should have.

[Attila Hajdrik (attilah)]

Ryan Cavanaugh (@RyanCavanaugh) FYI Salesforce Marketing Cloud is using an ES3 compatible language set for (Jint is their JS runtime) their SSJS language.

[Eric Robinson (ericdrobinson)]

Attila Hajdrik (@attilah) You might want to mention that over on #51909 which is explicitly about the ES3 target deprecation coming in TypeScript 5.0 (removal planned for 5.5).