Add browserslist depending js validation

[alexander-schranz]

To avoid the usage of JS functions which are not supported by some browsers we should introduce eslinter for this.

There exist a plugin for this type of linting:

npm install --save-dev eslint-plugin-compat

Based on the browserslist which can be dumped by running:

npx browserslist

and configured the following way in the project package.json:

    "browserslist": [
        "> 0.25% in my stats",
        "> 0.5% in CH",
        "last 3 version and not dead"
    ]

if a polyfill is added it can be configured the following way:

{
    "root": true,
    "extends": [
        // ...
        "plugin:compat/recommended"
    ],
    "settings": {
        "polyfills": [
            "fetch",
            "Object.values",
            "Object.assign",
            "Promise",
            "URL",
            "URLSearchParams",
            "Symbol",
            "Array.keys",
            "Array.from"
        ]
    },
    // ...
}

polyfills can mostly be included over the exist core-js or whatwg-fetch from github:

import 'whatwg-fetch';
import 'core-js/features/url';
import 'core-js/features/url-search-params';
import 'core-js/features/object/assign';
import 'core-js/features/object/values';
import 'core-js/features/promise';
import 'core-js/features/symbol';
import 'core-js/features/array/keys';
import 'core-js/features/array/from';