When I execute the command in listing 2.15 (MEAP_v4):
npm i bootstrap --save-prod]

bootstrap version 4.0.0 gets installed. However, the html and css snippets in the chapter are for bootstrap3.

Please install specific version of boostrap. Lateron in the text you refer to version 3.3.6, so i suggest to update listing 2.15 with:

npm i bootstrap@3.3.6 --save-prod]

In MEAP-v4 I read in appendix B section B.10 the following about decorators:

"While decorators were introduced to TypeScript a couple of years ago,
since they a still in the proposal stage for ECMAScript, decorators are still considered an
experimental feature of the language, and you need to turn on the
experimentalDecorators option during code compilation."

I think you remain implicit about the relationship between decorators in the two languages and it confuses me. I think you mean to say that decorators exist in Typescript, and they are proposed in ECMAScript. In order to properly transpile them, you need to turn on experimental features in the Typescript transpiler, like this:
"experimentalDecorators": true in tsconfig.json.

Please rephrase / clarify this fragment in the book, maybe elaborate a little bit on consequences for running the transpiled javasacript in browsers?