docs: Npm Packages guide for CLI (#19850)
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Ward Bell
Victor Berchet
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# Npm Packages
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Angular applications and Angular itself depend upon features and functionality provided by a variety of third-party packages.
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These packages are maintained and installed with the Node Package Manager (<a href="https://docs.npmjs.com/">npm</a>).
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The [**Angular CLI**](https://cli.angular.io/), Angular applications, and Angular itself depend upon features and functionality provided by libraries that are available as [**npm**](https://docs.npmjs.com/) packages.
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You can download and install these npm packages with the [**npm client**](https://docs.npmjs.com/cli/install), which runs as a node.js application.
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The [**yarn client**](https://yarnpkg.com/en/) is a popular alternative for downloading and installing npm packages.
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The Angular CLI uses `yarn` by default to install npm packages when you create a new project.
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<div class="l-sub-section">
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Node.js and npm are essential to Angular development.
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<a href="https://docs.npmjs.com/getting-started/installing-node" title="Installing Node.js and updating npm">
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Get them now</a> if they're not already installed on your machine.
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[Get them now](https://docs.npmjs.com/getting-started/installing-node "Installing Node.js and updating npm")
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if they're not already installed on your machine.
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**Verify that you are running node `v4.x.x` or higher and npm `3.x.x` or higher**
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by running the commands `node -v` and `npm -v` in a terminal/console window.
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@ -20,244 +22,152 @@ Consider using [nvm](https://github.com/creationix/nvm) for managing multiple
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versions of node and npm. You may need [nvm](https://github.com/creationix/nvm) if
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you already have projects running on your machine that use other versions of node and npm.
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</div>
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## _package.json_
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Both `npm` and `yarn` install packages identified in a [**package.json**](https://docs.npmjs.com/files/package.json) file.
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During [Setup](guide/setup), a <a href="https://docs.npmjs.com/files/package.json">package.json</a>
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file is installed with a comprehensive starter set of
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packages as specified in the `dependencies` and `devDependencies` sections.
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The CLI `ng new` command creates a default `packages.json` file for your project.
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This `packages.json` specifies _a starter set of packages_ that work well together and
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jointly support many common application scenarios.
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You can use other packages but the packages in _this particular set_ work well together and include
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everything you need to build and run the sample applications in this series.
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You will add packages to `packages.json` as your application evolves.
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You may even remove some.
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This guide focuses on the most important packages in the starter set.
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<div class="l-sub-section">
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#### *dependencies* and *devDependencies*
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Note: A cookbook or guide page may require an additional library such as *jQuery*.
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</div>
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You'll install more than you need for the QuickStart guide.
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No worries!
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You only serve to the client those packages that the application actually requests.
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This page explains what each package does. You can make substitutions later to suit your tastes and experience.
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## *dependencies* and *devDependencies*
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The `package.json` includes two sets of packages,
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[dependencies](guide/npm-packages#dependencies) and [devDependencies](guide/npm-packages#dev-dependencies).
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The *dependencies* are essential to *running* the application.
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The *devDependencies* are only necessary to *develop* the application.
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You can exclude them from production installations by adding `--production` to the install command, as follows:
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<code-example format="." language="bash">
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npm install my-application --production
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</code-example>
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{@a dependencies}
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## *dependencies*
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## *Dependencies*
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The `dependencies` section of `package.json` contains:
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* ***Features***: Feature packages give the application framework and utility capabilities.
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* **Angular packages**: Angular core and optional modules; their package names begin `@angular/`.
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* ***Polyfills***: Polyfills plug gaps in the browser's JavaScript implementation.
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* **Support packages**: 3rd party libraries that must be present for Angular apps to run.
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* ***Other***: Other libraries that support the application such as `bootstrap` for HTML widgets and styling.
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* **Polyfill packages**: Polyfills plug gaps in a browser's JavaScript implementation.
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### Angular Packages
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**@angular/animations**: Angular's animations library makes it easy to define and apply animation effects such as page and list transitions.
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Read about it in the [Animations guide](guide/animations).
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### Feature Packages
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**@angular/common**: The commonly needed services, pipes, and directives provided by the Angular team.
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The [`HttpClientModule`](guide/http) is also here, in the '@angular/common/http' subfolder.
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***@angular/core***: Critical runtime parts of the framework needed by every application.
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**@angular/core**: Critical runtime parts of the framework needed by every application.
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Includes all metadata decorators, `Component`, `Directive`, dependency injection, and the component lifecycle hooks.
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***@angular/common***: The commonly needed services, pipes, and directives provided by the Angular team.
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***@angular/compiler***: Angular's *Template Compiler*.
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**@angular/compiler**: Angular's *Template Compiler*.
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It understands templates and can convert them to code that makes the application run and render.
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Typically you don’t interact with the compiler directly; rather, you use it indirectly via `platform-browser-dynamic` or the offline template compiler.
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Typically you don’t interact with the compiler directly; rather, you use it indirectly via `platform-browser-dynamic` when [JIT compiling](guide/aot-compiler) in the browser.
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***@angular/platform-browser***: Everything DOM and browser related, especially
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**@angular/forms**: support for both [template-driven](guide/forms) and [reactive forms](guide/reactive-forms).
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**@angular/http**: Angular's old, soon-to-be-deprecated, HTTP client.
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**@angular/platform-browser**: Everything DOM and browser related, especially
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the pieces that help render into the DOM.
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This package also includes the `bootstrapStatic()` method
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for bootstrapping applications for production builds that pre-compile templates offline.
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for bootstrapping applications for production builds that pre-compile with [AOT](guide/aot-compiler).
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***@angular/platform-browser-dynamic***: Includes [Providers](api/core/Provider)
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and a [bootstrap](guide/ngmodule#bootstrap) method for applications that
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compile templates on the client. Don’t use offline compilation.
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Use this package for bootstrapping during development and for bootstrapping plunker samples.
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***@angular/http***: Angular's HTTP client.
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***@angular/router***: Component router.
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***@angular/upgrade***: Set of utilities for upgrading AngularJS applications to Angular.
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***[system.js](https://github.com/systemjs/systemjs)***: A dynamic module loader compatible with the
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[ES2015 module](http://www.2ality.com/2014/09/es6-modules-final.html) specification.
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Other viable choices include the well-regarded [webpack](https://webpack.github.io/).
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Your future applications are likely to require additional packages that provide
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HTML controls, themes, data access, and various utilities.
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**@angular/platform-browser-dynamic**: Includes [Providers](api/core/Provider)
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and methods to compile and run the app on the client
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using the [JIT compiler](guide/aot-compiler).
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**@angular/router**: The [router module](/guide/router) navigates among your app pages when the browser URL changes.
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**@angular/upgrade**: Set of utilities for upgrading AngularJS applications to Angular.
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{@a polyfills}
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### Polyfill packages
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Angular requires certain [polyfills](https://en.wikipedia.org/wiki/Polyfill) in the application environment.
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Install these polyfills using the npm packages that Angular lists in the *peerDependencies* section of its `package.json`.
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Many browsers lack native support for some features in the latest HTML standards,
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features that Angular requires.
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"[Polyfills](https://en.wikipedia.org/wiki/Polyfill)" can emulate the missing features.
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The [Browser Support](guide/browser-support) guide explains which browsers need polyfills and
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how you can add them.
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You must list these packages in the `dependencies` section of your own `package.json`.
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The default `package.json` installs the **[core-js](https://github.com/zloirock/core-js)** package
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which polyfills missing features for several popular browser.
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### Support packages
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<div class="l-sub-section">
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For background on this requirement, see [Why peerDependencies?](guide/npm-packages#why-peer-dependencies).
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</div>
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***core-js***: Patches the global context (window) with essential features of ES2015 (ES6).
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You may substitute an alternative polyfill that provides the same core APIs.
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When these APIs are implemented by the major browsers, this dependency will become unnecessary.
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***rxjs***: A polyfill for the [Observables specification](https://github.com/zenparsing/es-observable) currently before the
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**[rxjs](https://github.com/benlesh/RxJS)**: Many Angular APIs return _observables_. RxJS is an implementation of the proposed [Observables specification](https://github.com/zenparsing/es-observable) currently before the
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[TC39](http://www.ecma-international.org/memento/TC39.htm) committee that determines standards for the JavaScript language.
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You can pick a preferred version of *rxjs* (within a compatible version range)
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without waiting for Angular updates.
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***zone.js***: A polyfill for the [Zone specification](https://gist.github.com/mhevery/63fdcdf7c65886051d55) currently before the
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**[zone.js](https://github.com/angular/zone.js)**: Angular relies on zone.js to run Angular's change detection processes when native JavaScript operations raise events. Zone.js is an implementation of a [specification](https://gist.github.com/mhevery/63fdcdf7c65886051d55) currently before the
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[TC39](http://www.ecma-international.org/memento/TC39.htm) committee that determines standards for the JavaScript language.
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You can pick a preferred version of *zone.js* to use (within a compatible version range)
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without waiting for Angular updates.
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{@a other}
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### Other helper libraries
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***angular-in-memory-web-api***: An Angular-supported library that simulates a remote server's web api
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without requiring an actual server or real HTTP calls.
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Good for demos, samples, and early stage development (before you even have a server).
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***bootstrap***: [Bootstrap](http://getbootstrap.com/) is a popular HTML and CSS framework for designing responsive web apps.
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Some of the samples improve their appearance with *bootstrap*.
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{@a dev-dependencies}
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## *DevDependencies*
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The packages listed in the *devDependencies* section of the `package.json` help you develop the application on your local machine.
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You don't deploy them with the production application although there is no harm in doing so.
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**[@angular/cli](https://github.com/angular/angular-cli/)**: The Angular CLI tools.
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## *devDependencies*
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The packages listed in the *devDependencies* section of the `package.json` help you develop the application.
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You don't have to deploy them with the production application although there is no harm in doing so.
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**[@angular/compiler-cli](https://github.com/angular/angular/blob/master/packages/compiler-cli/README.md)**: The Angular compiler, which is invoked by the Angular CLI's `build` and `serve` commands.
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***[concurrently](https://www.npmjs.com/package/concurrently)***:
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A utility to run multiple *npm* commands concurrently on OS/X, Windows, and Linux operating systems.
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***[lite-server](https://www.npmjs.com/package/lite-server)***:
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A light-weight, static file server, by [John Papa](http://johnpapa.net/)
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with excellent support for Angular apps that use routing.
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**[@angular/language-service](https://github.com/angular/angular-cli/)**: The Angular language service analyzes component templates and provides type and error information that TypeScript-aware editors can use to improve the developer's experience.
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For example, see the [Angular language service extension for VS Code](https://marketplace.visualstudio.com/items?itemName=Angular.ng-template)
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***[typescript](https://www.npmjs.com/package/typescript)***:
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**@types/... **: TypeScript definition files for 3rd party libraries such as Jasmine and node.
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**[codelyzer](https://www.npmjs.com/package/codelyzer)**: A linter for Angular apps whose rules conform to the Angular [style guide](guide/styleguide).
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**jasmine/... **: packages to support the [Jasmine](https://jasmine.github.io/) test library.
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**karma/... **: packages to support the [karma](https://www.npmjs.com/package/karma) test runner.
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**[protractor](https://www.npmjs.com/package/protractor)**: an end-to-end (e2e) framework for Angular apps.
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Built on top of [WebDriverJS](https://github.com/SeleniumHQ/selenium/wiki/WebDriverJs).
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**[ts-node](https://www.npmjs.com/package/ts-node)**: TypeScript execution environment and REPL for node.
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**[tslint](https://www.npmjs.com/package/tslint)**: a static analysis tool that checks TypeScript code for readability, maintainability, and functionality errors.
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**[typescript](https://www.npmjs.com/package/typescript)**:
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the TypeScript language server, including the *tsc* TypeScript compiler.
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***@types/\* ***: TypeScript definition files.
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Learn more about it in the [TypeScript Configuration](guide/typescript-configuration#typings) guide.
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## So many packages! So many files!
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The default `package.json` installs more packages than you'll need for your project.
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{@a why-peer-dependencies}
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A given package may contain tens, hundreds, even thousands of files,
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all of them in your local machine's `node_modules` directory.
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The sheer volume of files is intimidating,
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You can remove packages that you don't need but how can you be sure that you won't need it?
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As a practical matter, it's better to install a package you don't need than worry about it.
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Extra packages and package files on your local development machine are harmless.
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## Why *peerDependencies*?
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There isn't a [*peerDependencies*](https://nodejs.org/en/blog/npm/peer-dependencies/) section in the QuickStart `package.json`.
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But Angular has a *peerDependencies* section in
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*its* `package.json`, which has important consequences for your application.
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This section explains why you load the [polyfill](guide/npm-packages#polyfills) *dependency*
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packages in the QuickStart application's `package.json`,
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and why you'll need those packages in your own applications.
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Packages depend on other packages. For example, your application depends on the Angular package.
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Two packages, "A" and "B", could depend on the same third package "C".
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"A" and "B" might both list "C" among their *dependencies*.
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What if "A" and "B" depend on different versions of "C" ("C1" and "C2"). The npm package system supports that.
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It installs "C1" in the `node_modules` folder for "A" and "C2" in the `node_modules` folder for "B".
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Now "A" and "B" have their own copies of "C" and they run without interferring with one another.
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But there is a problem. Package "A" may require the presence of "C1" without actually calling upon it directly.
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"A" may only work if *everyone is using "C1"*. It falls down if any part of the application relies on "C2".
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The solution is for "A" to declare that "C1" is a *peer dependency*.
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The difference between a `dependency` and a `peerDependency` is roughly this:
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>A **dependency** says, "I need this thing directly available to *me*."
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>
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>A **peerDependency** says, "If you want to use me, you need this thing available to *you*."
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The Angular `package.json` specifies several *peer dependency* packages,
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each pinned to a particular version of a third-party package.
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### You must install Angular's *peerDependencies* yourself.
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When *npm* installs packages listed in *your* `dependencies` section,
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it also installs the packages listed within *their* packages `dependencies` sections.
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The process is recursive.
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However, as of version 3, *npm* does *not* install packages listed in *peerDependencies* sections.
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This means that when your application installs Angular, ***npm* doesn't automatically install
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the packages listed in Angular's *peerDependencies* section**.
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Fortunately, *npm* issues a warning (a) When any *peer dependencies* are missing, or (b)
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When the application or any of its other dependencies
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installs a different version of a *peer dependency*.
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These warnings guard against accidental failures due to version mismatches.
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They leave you in control of package and version resolution.
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It is your responsibility to list all *peer dependency* packages **among your own *devDependencies***.
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<div class="l-sub-section">
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#### The future of *peerDependencies*
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The Angular polyfill dependencies are hard requirements. Currently, there is no way to make them optional.
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However, there is an npm feature request for "optional peerDependencies," which would allow you to model this relationship better.
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When this feature request is implemented, Angular will switch from *peerDependencies* to *optionalPeerDependencies* for all polyfills.
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</div>
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By default the Angular CLI build process bundles into a single file just the few "vendor" library files that your application actually needs.
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The browser downloads this bundle, not the original package files.
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See the [Deployment](guide/deployment) to learn more.
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