228 lines
12 KiB
Plaintext
228 lines
12 KiB
Plaintext
include ../_util-fns
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:marked
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Angular applications and Angular itself depend upon features and functionality provided by a variety of third-party packages (including Angular itself).
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These packages are maintained and installed with the Node Package Manager (<a href="https://docs.npmjs.com/" target="_blank">npm</a>).
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.l-sub-section
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:marked
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Don't have npm?
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<a href="https://docs.npmjs.com/getting-started/installing-node" target="_blank" title="Installing Node.js and updating npm">Get it now</a>
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because we're going to use it now and repeatedly throughout this documentation.
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:marked
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We recommend a comprehensive starter-set of packages as specified in the `dependencies` and `devDependencies`
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sections of the QuickStart
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<a href="https://docs.npmjs.com/files/package.json" target="_blank">package.json</a> file:
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+makeJson('quickstart/ts/package.1.json',{ paths: 'dependencies, devDependencies'}, 'package.json (dependencies)')(format=".")
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:marked
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There are other possible package choices and you're likely to add and subtract to meet your application needs.
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We're recommending *this particular set* because (a) we know they work well together and
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(b) they include everything we'll need to build and run the sample applications in this documentation series.
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.l-sub-section
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:marked
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*Almost* everything. A cookbook or guide chapter may require an additional library such as *jQuery*.
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:marked
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This is far more than we need for QuickStart.
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Indeed, it's more than we need for most applications.
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There is no harm in installing more than we need.
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We only serve to the client those packages that the application actually requests.
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In this chapter we explain what each package does and why we include it.
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Feel free to make substitutions later to suit your tastes and experience.
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.l-main-section
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:marked
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## *dependencies* and *devDependencies*
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The `package.json` distinguishes between two sets of packages,
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[dependencies](#dependencies) and [devDependencies](#dev-dependencies).
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The packages listed under *dependencies* are essential to *running* the application.
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The *devDependencies* are only necessary to *develop* the application.
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They can be excluded from production installations as in this example:
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code-example(format="." language="bash").
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npm install my-application --production
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a(id="dependencies")
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.l-main-section
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:marked
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## *dependencies*
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There are three package categories in the `dependencies` section of the application `package.json`:
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* ***Features*** - Feature packages provide our application with framework and utility capabilites.
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* ***Polyfills*** - Polyfills plug gaps in the browser's JavaScript implementation.
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* ***Other*** - Other libraries that support the application such as `bootstrap` for HTML widgets and styling.
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.l-main-section
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:marked
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### Feature Packages
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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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It understand templates and can convert them to code that makes the app run and render.
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Developers typically don’t interact with the compiler directly.
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They use it indirectly via `platform-browser-dynamic` or the offline template compiler.
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***@angular/platform-browser*** - Everything DOM and browser related, especially the pieces that help render into DOM.
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This package also includes the bootstrapStatic method for bootstrapping applications for production builds that pre-compile templates offline.
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***@angular/platform-browser-dynamic*** - Providers and a bootstrap method for applications that
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compile templates on the client. don’t use offline compilation.
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We use this package for boostrapping during development and for boostrapping 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 Angular 1 applications.
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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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There are other viable choices including the well-regarded [webpack](https://webpack.github.io/).
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SystemJS happens to be the one we use in the documentation samples. It works.
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Our 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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a(id="polyfills")
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.l-main-section
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:marked
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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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We install these polyfills with very specific npm packages that Angular lists in the *peerDependencies* section of its `package.json`.
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We must list these packages in the `dependencies` section of our own `package.json`.
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.l-sub-section
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:marked
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See "[Why peerDependencies?](#why-peer-dependencies)" below for background on this requirement.
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:marked
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***core-js*** - monkey patches the global context (window) with essential features of ES2015 (ES6).
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Developers may substitute an alternative polyfill that provides the same core APIs.
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This dependency should go away once these APIs are implemented by all supported ever-green browsers.
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***reflect-metadata*** - a dependency shared between Angular and the ***TypeScript compiler***.
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Developers should be able to update a TypeScript package without upgrading Angular,
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which is why this is a dependency of the application and not a dependency of Angular.
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***rxjs*** - a polyfill for the [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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Developers should be able to 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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[TC39](http://www.ecma-international.org/memento/TC39.htm) committee that determines standards for the JavaScript language.
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Developers should be able to 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(id="other")
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.l-main-section
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:marked
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### Other helper libraries
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***angular2-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, documentation samples, and early stage development (before we even have a server).
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Learn about it in the [Http Client](server-communication.html#appendix-tour-of-heroes-in-memory-server) chapter.
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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 documentation samples improve their appearance with *bootstrap*.
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a(id="dev-dependencies")
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.l-main-section
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:marked
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## *devDependencies*
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The packages listed in the *devDependencies* section of the `package.json` help us develop the application.
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They do not have to be deployed with the production application although there is rarely harm in doing so.
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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, written and maintained by [John Papa](http://johnpapa.net/)
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with excellent support for Angular apps that use routing.
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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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***[typings](https://www.npmjs.com/package/typings)*** - a manager for TypeScript definition files.
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Learn more about it in the [TypeScript Configuration](typescript-configuration.html#typings) chapter.
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This section likely grows as we add more tools, testing, and build support.
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The QuickStart set is sufficient for developing the documentation sample applications.
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.l-main-section
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a(id="why-peer-dependencies")
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:marked
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## Why *peerDependencies*?
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We don't have a *peerDependencies* section in the QuickStart `package.json`.
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But Angular itself has a *peerDependencies* section in
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[*its* package.json](https://github.com/angular/angular/blob/master/modules/angular2/package.json)
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and that has important consequences for our application.
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It explains why we load the [polyfill](#polyfills) *dependency* packages in the QuickStart `package.json`,
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and why we'll need those packages in our own applications.
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Let's briefly explain what [peer dependencies](https://nodejs.org/en/blog/npm/peer-dependencies/) are about.
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As we know, packages depend on other packages. For example, our application depends upon 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. This is great.
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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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Angular finds itself in this situation.
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Accordingly, 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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### We must install Angular's *peerDependencies* ourselves
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When *npm* installs packages listed in *our* `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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But as of version 3, *npm* does *not* install packages listed in *peerDependencies* sections.
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That means when our application installs Angular, ***npm* will not automatically install
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the packages listed in Angular's *peerDependencies* section**.
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Fortunately, *npm* warns us (a) when any *peer dependencies* are missing or (b)
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when the application or any its other dependencies
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installs a different version of a *peer dependency*.
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These warnings are a critical guard against accidental failures due to version mismatches.
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They leave us in control of package and version resolution.
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It is our responsibility to list all *peer dependency* packages **among our own *devDependencies***.
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.l-sub-section
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:marked
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#### The future of *peerDependencies*
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The Angular polyfill dependencies should be just a suggestion or a hint to developers so that they know what Angular expects.
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They should not be hard requirements as they are today. We don't have a way to make them optional today.
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There is a npm feature request for "optional peerDependencies" which would allow us to model this relationship better.
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Once implemented, Angular will switch from *peerDependencies* to *optionalPeerDependencies* for all polyfills.
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