Should we compile to ES2018 in Lumino 2?

[afshin]

It seems as though the browsers we support all support ES2018: https://caniuse.com/?search=ES2018

I propose switching to ES2018 as our compilation target:

lumino/tsconfigbase.json

Line 21 in b603dd3

"target": "ES6",

What do you think?

Pathological case

Out of curiosity, I looked to see how the [Symbol.asyncIterator] function in Poll compiled.

TypeScript source

async *[Symbol.asyncIterator](): AsyncIterableIterator<IPoll.State<T, U, V>> {
  while (!this.isDisposed) {
    yield this.state;
    await this.tick.catch(() => undefined);
  }
}

Compiled with ES6 target

[Symbol.asyncIterator]() {
  return __asyncGenerator(this, arguments, function* _a() {
      while (!this.isDisposed) {
          yield yield __await(this.state);
          yield __await(this.tick.catch(() => undefined));
      }
  });

Compiled with ES2018 target

async *[Symbol.asyncIterator]() {
  while (!this.isDisposed) {
      yield this.state;
      await this.tick.catch(() => undefined);
  }
}

---

This case is particularly egregious but all uses of await are wrapped in the ES6 version and native in the ES2018 version. We use await extensively in the @lumino/application and @lumino/polling packages.

---

Please 👍 if you agree and 👎 if you disagree.

[blink1073]

Looking at the ECMAScript 2016+ compatibility table, it looks like among the browsers we support, async generators are available (and most other ECMAScript features to that point as well). The only limitation I see is that Safari is missing support for RegExp Lookbehind Assertions.