190 lines
9.7 KiB
Plaintext
190 lines
9.7 KiB
Plaintext
include ../_util-fns
|
|
|
|
:marked
|
|
Angular applications and Angular itself depend upon features and functionality provided by a variety of third-party packages
|
|
maintained and installed with the Node Package Manager (<a href="https://docs.npmjs.com/" target="_blank">npm</a>).
|
|
.l-sub-section
|
|
:marked
|
|
Don't have npm?
|
|
<a href="https://docs.npmjs.com/getting-started/installing-node" target="_blank" title="Installing Node.js and updating npm">Get it now</a>
|
|
because we're going to use it now and repeatedly throughout this documentation.
|
|
:marked
|
|
The Angular team recommends the starter-set of packages specified in the `dependencies` and `devDependencies`
|
|
sections of the QuickStart
|
|
<a href="https://docs.npmjs.com/files/package.json" target="_blank">package.json</a> file:
|
|
+makeJson('quickstart/ts/package.1.json',{ paths: 'dependencies, devDependencies'}, 'package.json (dependencies)')(format=".")
|
|
:marked
|
|
There are other possible package choices.
|
|
We're recommending this particular set that we know work well together.
|
|
|
|
In this chapter we explain what each package does and why we include it.
|
|
Feel free to make substitutions later to suit your tastes and experience.
|
|
|
|
.l-main-section
|
|
:marked
|
|
## *dependencies* and *devDependencies*
|
|
The `package.json` distinguishes between two sets of packages,
|
|
[dependencies](#dependencies) and [devDependencies](#dev-dependencies).
|
|
|
|
The packages listed under *dependencies* are essential to *running* the application.
|
|
The *devDependencies* are only necessary to *develop* the application.
|
|
They can be excluded from production installations as in this example:
|
|
code-example(format="." language="bash").
|
|
npm install my-application --production
|
|
|
|
a(id="dependencies")
|
|
.l-main-section
|
|
:marked
|
|
## *dependencies*
|
|
There are two package categories in the `dependencies` section of the application `package.json`:
|
|
|
|
* ***Features*** - Feature packages provide our application with framework and utility capabilites.
|
|
|
|
* ***Polyfills*** - Polyfills plug gaps in the browser's JavaScript implementation.
|
|
|
|
.l-main-section
|
|
:marked
|
|
### Feature Packages
|
|
|
|
***angular2*** - The framework we know and love; the reason we're all here.
|
|
|
|
***[system.js](https://github.com/systemjs/systemjs)*** - A dynamic module loader compatible with the
|
|
[ES2015 module](http://www.2ality.com/2014/09/es6-modules-final.html) specification.
|
|
There are other viable choices including the well-regarded [webpack](https://webpack.github.io/).
|
|
SystemJS happens to be the one we use in the documentation samples. It works.
|
|
|
|
Our applications are likely to require additional packages that provide
|
|
HTML controls, themes, data access, and various utilities.
|
|
|
|
|
|
a(id="polyfills")
|
|
.l-main-section
|
|
:marked
|
|
### Polyfill Packages
|
|
|
|
Angular requires certain [polyfills](https://en.wikipedia.org/wiki/Polyfill) in the application environment.
|
|
We install these polyfills with very specific npm packages that Angular lists in the *peerDependencies* section of its `package.json`.
|
|
|
|
We must list these packages in the `dependencies` section of our own `package.json`.
|
|
|
|
.l-sub-section
|
|
:marked
|
|
See "[Why peerDependencies?](#why-peer-dependencies)" below for background on this requirement.
|
|
:marked
|
|
***es6-promise*** - Angular applications require ES2015 promise support.
|
|
Although some browsers provide a native implementation of ES2015 promises many do not.
|
|
We still need this library even for the browsers that do support promises
|
|
in order to integrate with the current version of *zone.js* (see below).
|
|
This integration dependency goes away in the next version of *zone.js*
|
|
The need for *es6-promise* should disappear entirely once promises are implemented by all supported ever-green browsers.
|
|
|
|
***es6-shim*** - monkey patches the global context (window) with essential features of ES2016 (ES6).
|
|
Developers may substitute an alternative polyfill that provides the same core APIs.
|
|
This dependency should go away once these APIs are implemented by all supported ever-green browsers.
|
|
|
|
***reflect-metadata*** - a dependency shared between Angular and the ***TypeScript compiler***.
|
|
Developers should be able to update a TypeScript package without upgrading Angular,
|
|
which is why this is a dependency of the application and not a dependency of Angular.
|
|
|
|
***rxjs*** - a polyfill for the [Observables specification](https://github.com/zenparsing/es-observable) currently before the
|
|
[TC39](http://www.ecma-international.org/memento/TC39.htm) committee that determines standards for the JavaScript language.
|
|
Developers should be able to pick a preferred version of *rxjs* (within a compatible version range)
|
|
without waiting for Angular updates.
|
|
|
|
***zone.js*** - a polyfill for the [Zone specification](https://gist.github.com/mhevery/63fdcdf7c65886051d55) currently before the
|
|
[TC39](http://www.ecma-international.org/memento/TC39.htm) committee that determines standards for the JavaScript language.
|
|
Developers should be able to pick a preferred version of *zone.js* to use (within a compatible version range)
|
|
without waiting for Angular updates.
|
|
|
|
a(id="dev-dependencies")
|
|
.l-main-section
|
|
:marked
|
|
## *devDependencies*
|
|
The packages listed in the *devDependencies* section of the `package.json` help us develop the application.
|
|
They do not have to be deployed with the production application although there is rarely harm in doing so.
|
|
|
|
***[concurrently](https://www.npmjs.com/package/concurrently)*** -
|
|
a utility to run multiple *npm* commands concurrently on OS/X, Windows, and Linux operating systems.
|
|
|
|
***[lite-server](https://www.npmjs.com/package/lite-server)*** -
|
|
a light-weight, static file server, written and maintained by [John Papa](http://johnpapa.net/)
|
|
with excellent support for Angular apps that use routing.
|
|
|
|
***[typescript](https://www.npmjs.com/package/typescript)*** -
|
|
the TypeScript language server including the *tsc* TypeScript compiler.
|
|
|
|
***[typings](https://www.npmjs.com/package/typings)*** - a manager for TypeScript definition files.
|
|
Learn more about it in the [TypeScript Configuration](typescript-configuration.html#typings) chapter.
|
|
|
|
This section likely grows as we add more tools, testing, and build support.
|
|
The QuickStart set is sufficient for developing the documentation sample applications.
|
|
|
|
.l-main-section
|
|
a(id="why-peer-dependencies")
|
|
:marked
|
|
## Why *peerDependencies*?
|
|
|
|
We don't have a *peerDependencies* section in the QuickStart `package.json`.
|
|
But Angular itself has a *peerDependencies* section in
|
|
[*its* package.json](https://github.com/angular/angular/blob/master/modules/angular2/package.json)
|
|
and that has important consequences for our application.
|
|
|
|
It explains why we load the [polyfill](#polyfills) *dependency* packages in the QuickStart `package.json`,
|
|
and why we'll need those packages in our own applications.
|
|
|
|
Let's briefly explain what [peer dependencies](https://nodejs.org/en/blog/npm/peer-dependencies/) are about.
|
|
|
|
As we know, packages depend on other packages. For example, our application depends upon the Angular package.
|
|
|
|
Two packages, 'A' and 'B', could depend on the same third package 'C'.
|
|
'A' and 'B' might both list 'C' among their *dependencies*.
|
|
|
|
What if 'A' and 'B' depend on different versions of 'C' ('C1' and 'C2'). The npm package system supports that!
|
|
It installs 'C1' in the `node_modules` folder for 'A' and 'C2' in the `node_modules` folder for 'B'.
|
|
Now 'A' and 'B' have their own copies of 'C' and they run without interferring. This is great.
|
|
|
|
But there is a problem. Package 'A' may require the presence of 'C1' without actually calling upon it directly.
|
|
'A' may only work if *everyone is using 'C1'*. It falls down if any part of the application relies on 'C2'.
|
|
|
|
The solution is for 'A' to declare that 'C1' is a *peer dependency*.
|
|
|
|
The difference between a `dependency` and a `peerDependency` is roughly this:
|
|
|
|
>A **dependency** says, "I need this thing directly available to *me*."
|
|
>
|
|
>A **peerDependency** says, "if you want to use me, you need this thing available to *you*."
|
|
|
|
Angular finds itself in this situation.
|
|
Accordingly, the Angular `package.json` specifies several *peer dependency* packages,
|
|
each pinned to a particular version of a third-party package.
|
|
|
|
### We must install Angular's *peerDependencies* ourselves
|
|
|
|
When *npm* installs packages listed in *our* `dependencies` section,
|
|
it also installs the packages listed within *their* packages `dependencies` sections.
|
|
The process is recursive.
|
|
|
|
But as of version 3, *npm* does *not* install packages listed in *peerDependencies* sections.
|
|
|
|
That means when our application installs Angular, ***npm* will not automatically install
|
|
the packages listed in Angular's *peerDependencies* section**.
|
|
|
|
Fortunately, *npm* warns us (a) when any *peer dependencies* are missing or (b)
|
|
when the application or any its other dependencies
|
|
installs a different version of a *peer dependency*.
|
|
|
|
These warnings are a critical guard against accidental failures due to version mismatches.
|
|
They leave us in control of package and version resolution.
|
|
|
|
It is our responsibility to list all *peer dependency* packages **among our own *devDependencies***.
|
|
|
|
.l-sub-section
|
|
:marked
|
|
#### The future of *peerDependencies*
|
|
|
|
The Angular polyfill dependencies should be just a suggestion or a hint to developers so that they know what Angular expects.
|
|
They should not be hard requirements as they are today. We don't have a way to make them optional today.
|
|
|
|
There is a npm feature request for "optional peerDependencies" which would allow us to model this relationship better.
|
|
Once implemented, Angular will switch from *peerDependencies* to *optionalPeerDependencies* for all polyfills.
|