Why do we have install Node.js for Angular 2.0?

Because Anglar2 is based on Typescript, Web Components and ES6 which need compilation for performance and broader browser support. Typescript is compiled to ES5 JavaScript and the other features require shims for backwards compatibility.

Since Typescript is a superset of JavaScript, and it's compiled to JavaScript anyway, you can write your code in plain JavaScript but it's not recommended.

For a more detailed explanation check out these videos on YouTube

• Why Typescript
• Instalation steps

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.

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Footnote: there's a similar question about needing Node.js for AngularJS (1.x).

NodeJS gives you the tool npm that allows you to download libraries and packages you would use in Angular 2. From the shell you can go to your folder and type npm install to install dependencies you need to have installed to get your angular project going. It will make it easier for you! If you want a complete starter kit go to https://github.com/buckyroberts, you can fork or download the zip with all the starter files to get you going :)