Technically, Node.js and NPM are not needed to do Angular2 work. It does ease things though. Here’s the main reasons I speculate are behind this choice:
-
CLI: Since a while now the de facto way to build and develop new Angular apps is to use the CLI tooling which relies on Node and NPM as well.
-
TypeScript: Examples are .ts, and you need to run a compiler step to get them into .js, which can be done on-the-fly easily with Node.js and NPM (plus it’s a way of easily getting typing files);
- Web Server: Serving your Angular SPA from a “real” albeit light web server prevents probably some nasty issues that come with checking your site using
file://links.
The Quickstart guide itself actually continues to mention some more concrete reasons as well:
Here’s what these scripts do:
npm start– runs the compiler and a server at the same time, both in “watch mode”
npm run tsc– runs the TypeScript compiler once
npm run tsc:w– runs the TypeScript compiler in watch mode; the process keeps running, awaiting changes to TypeScript files and re-compiling when it sees them
npm run lite– runs the lite-server, a light-weight, static file server with excellent support for Angular apps that use routing
npm run typings– runs the typings tool separately
npm run postinstall– called by npm automatically after it successfully completes package installation. This script installs the TypeScript definition files defined in typings.json
You can also have a look at the Quickstart source and further dive into where NPM is needed.
Footnote: there’s a similar question about needing Node.js for AngularJS (1.x).