https://angular.io/guide/npm-packages
使用angular cli指令行ng new建立一個新的angular項目後，目錄結構如下：
展開node_modules檔案夾，進而展開@angular子檔案夾：
@angular/animations:angular’s animations library makes it easy to define and apply animation effects such as page and list transitions.
@angular/common: the commonly-needed services, pipes, and directives provided by the angular team. the httpclientmodule is also here, in the @angular/common/http subfolder.
@angular/compiler:angular’s template compiler. it understands templates and can convert them to code that makes the application run and render. typically you don’t interact with the compiler directly; rather, you use it indirectly via platform-browser-dynamic when jit compiling in the browser.
@angular/core:critical runtime parts of the framework that are needed by every application. includes all metadata decorators, component, directive, dependency injection, and the component lifecycle hooks.
@angular/forms: support for both template-driven and reactive forms. for information about choosing the best forms approach for your app, see introduction to forms.
@angular/
platform‑browser: everything dom and browser related, especially the pieces that help render into the dom. this package also includes the bootstrapmodulefactory() method for bootstrapping applications for production builds that pre-compile with aot.
platform‑browser‑dynamic: includes providers and methods to compile and run the app on the client using the jit compiler.
@angular/router: the router module navigates among your app pages when the browser url changes.