refactor: static createInstance for wider browser support

[belgattitude]

Reason: i18next 23 dropped support for older node and browsers.... The new version runs fine with recent node, but I feel there's an issue regarding the transpilation of

class I18n extends EventEmitter {
  static createInstance = (options = {}, callback) => new I18n(options, callback)
}

It's currently transpiled as

class em extends D {
            static createInstance = function ()  {
                let e = arguments.length > 0 && void 0 !== arguments[0] ? arguments[0] : {},
                    t = arguments.length > 1 ? arguments[1] : void 0;
                return new em(e, t)
            };
}

Runs fine from es2022 (not before) ... but browser support I'm less sure how static + function will work (https://caniuse.com/mdn-javascript_classes_static -> 95% / but I suspect that static = function is a different case).

With this PR the transpiled code would be

            static createInstance()  {
                let e = arguments.length > 0 && void 0 !== arguments[0] ? arguments[0] : {},
                    t = arguments.length > 1 ? arguments[1] : void 0;
                return new em(e, t)
            };

Which:

• allow to pass from es2019 to es2022 checks (difficult to exactly refer to node versions, but let's says node 14 is es2020 100% compat)
• keep the browser baseline at threshold of 95%

Need to dig more...

PS: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes/static

Checklist

• only relevant code is changed (make a diff before you submit the PR)
• run tests npm run test
• tests are included
• commit message and code follows the Developer's Certification of Origin

[coveralls]

coverage: 92.332% (-0.004%) from 92.336% when pulling b684f7d on belgattitude:refactor-static-instance into c45439e on i18next:master.

[belgattitude]

@adrai do you think this change is equivalent ? In my understanding yes. (no late static binding issue, no async, no need for the function / class property), but I guess there is or was a reason..

[adrai]

we may ask @perrin4869 => e401175

[perrin4869]

Looks equivalent to me!
I generally prefer to use arrow functions because it saves the need to use curly braces, so it was probably only an esthetics decision, feel free to change it 🙂

[belgattitude]

@perrin4869 to give you a bit of context... in the latest I18next v23 we don't transpile for older browser/platforms... but the notation with static xxx = function might bring some issues (does not pass eschecks before es2022). So the idea here is to refactor at the source. See also https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes/static

[belgattitude]

Thank you so much @perrin4869 !

[belgattitude]

@adrai on my side it seems okay... feel free to merge whenever needed. I'll dig into other issues in the coming days

[adrai]

thank you @belgattitude and @perrin4869 v23.0.2 has just been released