Some history:
* `uglifyjs-webpack-plugin` < v1.0 used the minifier `uglify-js`
* however `uglify-js` does not support ES6, which resulted in a fork
called `uglify-es` that was developed in the `uglify-js` repository,
but under the `harmony` branch
* `uglifyjs-webpack-plugin` v1.x switched to `uglify-es` for ES6 support
* however `uglify-es` stopped being maintained:
https://github.com/mishoo/UglifyJS2/issues/3156#issuecomment-392943058
* which led to a fork called `terser` that has incorporated all of
the unmerged PRs and will be where all new development occurs:
https://github.com/fabiosantoscode/terser
* `terser-webpack-plugin` was created, which is the `terser` equivalent
of `uglifyjs-webpack-plugin`:
https://github.com/webpack-contrib/terser-webpack-plugin
* `uglifyjs-webpack-plugin` v2.x will be switching back to `uglify-js`,
so any project that needs to support ES6 now needs to switch to
`terser-webpack-plugin`.
Fixes#7923.
Some history:
* `uglifyjs-webpack-plugin` < v1.0 used the minifier `uglify-js`
* however `uglify-js` does not support ES6, which resulted in a fork
called `uglify-es` that was developed in the `uglify-js` repository,
but under the `harmony` branch
* `uglifyjs-webpack-plugin` v1.x switched to `uglify-es` for ES6 support
* however `uglify-es` stopped being maintained:
https://github.com/mishoo/UglifyJS2/issues/3156#issuecomment-392943058
* which led to a fork called `terser` that has incorporated all of
the unmerged PRs and will be where all new development occurs:
https://github.com/fabiosantoscode/terser
* `terser-webpack-plugin` was created, which is the `terser` equivalent
of `uglifyjs-webpack-plugin`:
https://github.com/webpack-contrib/terser-webpack-plugin
* `uglifyjs-webpack-plugin` v2.x will be switching back to `uglify-js`,
so any project that needs to support ES6 now needs to switch to
`terser-webpack-plugin`.
Fixes#7923.
Running node_modules/bin/webpack without webpack-cli installed will get hang.
The culprit is that webpack expects a stdin of whether to install webpack-cli or not. However, as examples/build-common use `child_process.exec` to execute `webpack`, the user will not be prompted for any questions since the stdin is not piped and the stdout will be pass to parent process only after the child process exits. We can keep build-common simple by instructing devs to install webpack-cli before they build examples.
Also rewrite the install step using yarn since we use yarn in webpack.