Discovering new angular/cli command — library. Short overview.

When a number of the projects grows, it becomes necessary to somehow re-use not only the modules with the code but also the UI components themselves. There are many options for solving this problem — from the traditional copy-paste approach to setting up a separate project with tests, documentation and whatever you need.

But the second option requires significant efforts to start and each such project is unique — with its own tools in which each new developer have to invest time and efforts. At the end of July, the Angular Team proposed a comprehensive solution for that problem — new command to the angular/cli — library.

Let’s see what they did.

For tests, I take the most recent stable version of angular/cli is taken — 6.1.5 (04/09/2018)

Jumping in the perfect world

In a perfect world, everything should be comfortable. So, for the component library, I would suggest three important points.

  • Uniformity of projects and quick start
  • Comfortable development
  • Comfortable distribution

So, let’s start

To create a new library, we need to make two steps: create a new project and add a library inside. Firstly, create a new project:

npx @angular/cli@6.1.5 new mylibapp

I’m using npx to avoid global installation and “npm run” constructs. If you have npm version 5.2 or later, try it. You can read more from here

After executing the command, you will see a standard (for Angular 6, which quite differs from the 5th version) project with two internal subprojects — the main project “mylibapp” and project with end2end tests — “mylibapp-e2e”.

As you can see, there is no library yet.

And here it is the first nuance. Our name is already occupied by the main project, and it will not be possible to name the library either. Therefore, if you want to name the library like “my-super-library”, firstly you need to create a project that should be called something different. For example, “my-super-library-project”. And only then, you can safely create a library with the desired name.

Now, let’s create the new library.

cd mylibapp
npx ng generate library mylib --prefix mlb

You don’t have to use prefix option, but I highly recommend this to avoid possible collisions with other libraries.

As you can see, now we got a new, 3rd sub-project — library. It has it’s own package.json, tsconfig и karma.conf.js files, so we can easily configure it without any risks to damage other projects. It is good, but for some reason, our new library is not a standalone project. This leads to the existence of the not used code in the repo what is not good. And if we can remove e2e project more-less easily I can’t say the same about the main project.

Now let’s see what tools we get out of the box. They are

This is a standard toolset for angular projects without anything specific to the library. This is a little bit disappointing because some tools for viewing components and rendering them into documentation (for example storybook) would be really nice to have. But okay, let’s assume that we just left room for maneuver.

Let’s run some tests to make sure that everything works.

npm test mylib
npx ng lint mylib

I did it without any problems, but for some reason, Chrome was used as a testing browser. I have nothing against Chrome, but on the build servers, you will probably not see it. Why not use Puppeteer as a headless browser instead is unclear.

Let’s summarize

Pros

  • Quick start of the new project
  • Uniform approach for all new libraries

Cons

  • Unneeded code in the project
  • Crucial tools should be added manually

So far so good, let’s go further

Do you know? If you need, you can generate any number of libraries you need inside one project. each of them will have a separate config and publish setup.

Development

Ok, we created a new library and already have some UI components inside as an example. So let’s try to see them. As far as we don’t get any tool for that, let’s use the original project. So, to see something we need to make two steps

  • Build the library
  • Import library module into the main project

Building works just as in usual angular project

npx ng build mylib

And importing is also simple:

import { MylibModule } from "mylib";
...
@NgModule({
declarations: [
AppComponent,
],
imports: [
BrowserModule, MylibModule
],
providers: [],
bootstrap: [AppComponent]
})

And don’t forget to add the new component from the library inside the main component, like this

app.component.html

<mlb-mylib></mlb-mylib>

Now, start the main application and you should see the result. Looks ok, but one more problem appears — current @angular/cli version (6.1.5) doesn’t support watch mode for the libraries. This will be fixed in later versions, but right now it is also disappointing.

So, let’s add the new component to the library. To do this we can use standard angular/cli syntax, but with special flag named — project. As far as the library is our main project and most of the time we will add something to it, this can become a bit of annoying.

npx ng generate component some-nice-image --project mylib

Now, let’s add an image inside our component. Under mylib/src create the new folder with name assets, add some picture and add an image tag inside some-nice-image component

<img alt="image was not found" src="../../assets/myimage.png" />

Rebuild the library again to see the result. But, surprise, — there is no image on the screen and there is no image inside the build folder. This happened not because we did a mistake in the path — but because right now, library project doesn’t support static resources by default. To work with them you need to copy them manually or use this workaroung what is also not very comfortable.

But, one very cool feature should work just out of the box — tree shaking! So let’s test it. Create a new component with some big text inside but don’t use it in the main project.

npx ng generate component big --project mylib
npm run build --prod

And you will see that the size of the library’s bundle increased, but the size of the main project’s bundle — not! That’s the really great feature!

Next step is to test adding dependencies inside the library. Because of all subprojects have own package.json we need to dive into the project folder and execute npm install command

npm i -D @drag13/when-do
npm i @drag13/round-to

I specifically put them in different ways to check how the packer handles this later. Install was successful, but if you try to rebuild library you will get a warning

Distributing npm packages with ‘dependencies’ is not recommended. Please consider adding ‘drag13 / round-to’ peerDependencies’or remove it from ‘dependencies

and, then, and the error:

Dependency @drag13/round-to-be must explicitly be whitelisted

This is quite a new behavior. By design, a library doesn’t want to have direct dependencies. Only dev and peer dependencies allowed by default. To resolve this issue we need to install the desired dependencies in the main project or edit an ng-package.json file to whitelist this dependency. This is done to reduce the number of dependencies of the library users.

All other works as in usual Angular project.

Short summary

Pros

  • Working in the known framework with already known commands
  • Tree shaking feature comes out of the box

Cons

  • To see the component we need to use the main project
  • No watch mode for now
  • No static resources support out of the box

Publish

This is the best part of the whole process. Publish is great and extremely easy. For publishing purposes, Angular took the well-known tool — ng-packgr. It will handle minification, bundling, generating new package.json for the project and all other boring stuff. Let’s try!

npx ng build --prod
cd dist/mylib
npm pack

I changed npm publish to npm pack to avoid putting test code to the real npm. But when you will be ready — just change “pack” to “publish” and all will be great.

Firstly, let’s examine package.json

As you can see, it looks like not real package.json from our library. It has path to types, the path to the main file and other useful meta information. Also, devDependencies was not cleaned, so keep this in mind.

Secondly, let’s quickly review what is inside the package

As you see, package contains some bundles (minified and non-minified bundle in universal module definition format inside), types in d.ts files and bundles in some special angular formats like fest5 and fesm2015. Also it contains some other metadata needed to integrate library into the consumer project.

But what is the most interesting that you don’t even need to know all that to publish your library. The only thing you need — write good code, and this is great!

Summary

The solution is quite good, but still not polished. Starting and publishing steps are done well, but the development part has some problems such as redundant code, no support for the assets an so on. And the root of this problem is that library was not designed as a standalone project.

Despite this, Angular library is a promising solution and can be taken as a starting point right after watch mode will be added.

Hope you found this overview interesting and useful, have a nice day!