Provide Internet Explorer support

Tip submitted by @wmarques & @anthony-o

JHipster supports only evergreen browsers. However you can still easily support some older browsers like Internet Explorer.

In order to do that you have to:

1. Set target to es5 in your tsconfig
2. Then you have two options:
   1. Add the correct polyfills from ‘core-js’, if you don’t know which one you should use, check the Angular CLI project and their polyfills.
   2. Or use babel + Babel preset-env to automatically import the correct core-js polyfills based on a browserslist file.

Full tip using Babel

First, add those package.json dependencies: @babel/core, @babel/preset-env and babel-loader. Example with yarn:

yarn add @babel/core @babel/preset-env babel-loader --exact --dev

(tested with the following versions for a working IE11 version on a JHipster v6.3.1 generated application:

    "@babel/core": "7.6.4",
    "@babel/preset-env": "7.6.3",
    "babel-loader": "8.0.6",

)

Now add the following lines at the top of src/main/webapp/app/polyfills.ts:

import 'core-js/stable';
import 'regenerator-runtime/runtime';

In webpack/webpack.common.js, after

            {
                test: /manifest.webapp$/,
                loader: 'file-loader',
                options: {
                    name: 'manifest.webapp'
                }
            },

add the following lines:

            {
                test: /\.js/,
                use: {
                  loader: 'babel-loader',
                  options: {
                    "presets": [
                      [
                        "@babel/preset-env",
                        {
                          "targets": {
                            "firefox": "60",
                            "ie": "11"
                          },
                          "useBuiltIns": "entry",
                          "corejs": 3
                        }
                      ]
                    ]
                  }
                },
                exclude: /@babel(?:\/|\\{1,2})runtime|core-js/,
              },

And finally, change target to es5 in tsconfig.json & tsconfig-aot.json.

See this GitHub issue & this SO answer for more details.