This library is in early alpha and has not yet reached enough maturity to promise backward compatibility of interfaces.
This is a simple library 22ndtech, implementing the Angular Package Format v4.0.
Currently only unscoped, primary entry-point libraries are supported.
- a simple example library
- unit tests for the library
- a demo application that consumes the library in JIT mode and runs in watch mode
- an integration app that consumes the library in JIT and AOT mode and runs e2e tests
Common tasks are present as npm scripts:
npm startto run a live-reload server with the demo app
npm run testto test in watch mode, or
npm run test:onceto only run once
npm run buildto build the library
npm run lintto lint
npm run cleanto clean
npm run integrationto run the integration e2e tests
npm install ./relative/path/to/libafter
npm run buildto test locally in another app
If you need to debug the integration app, please check
What's in the 22ndtech Library?
The 22ndtech library contains a similar structure to the Quickstart seed. It's modified to build and test a library instead of an application.
Consequently, there are many different files in the project.
Focus on the following TypeScript (
.ts) files in the
src/ ├── demo/ | └── app/ | ├── app.component.ts | └── app.module.ts └── lib/ ├── index.ts └── src/ ├── component/ | └── lib.component.ts ├── service/ | └── lib.service.ts └── module.ts
Each file has a distinct purpose and evolves independently as the application grows.
src/ concern building, deploying, and testing your app.
They include configuration files and external dependencies.
src/lib/ "belong" to your library, while
src/demo/ contains a demo application
that loads your library.
Libraries do not run by themselves, so it's very useful to have this "demo" app while developing to see how your library would look like to consumers.
When you run
npm start, the demo application is served.
The following are all in
The build step
You can build the library by running
npm run build.
This will generate a
dist/ directory with all the entry points described above.
All the logic for creating the build can be found in
./build.js. It consists of roughly 5 steps:
- Compile with the AOT Compiler (AOT compiler or
ngc) for ES5 and ES2015.
- Copy typings, metatada, html and css.
- Create each bundle using Rollup.
While testing is always important, it's especially important in libraries because consumer applications might break due to bugs in libraries.
But the fact that a library is consumed by another application is also what makes it hard to test.
To properly test a library, you need to have an integration tests. An integration test is to libraries what an end-to-end test is to applications. It tests how an app would install and use your library.
The 22ndtech Library includes a directory called
integration containing a standalone
app that consumes your built library in both AOT and JIT modes, with end-to-end tests to verify
To run the integration tests, do
npm run integration which does the following:
- Build your library.
- Enter the integration app's directory.
- Install dependencies.
- Build the app in AOT mode.
- Test the app in AOT mode.
- Test the app in JIT mode.
Running integration tests gives you greater confidence that your library is properly built.
In addition to integration tests, you can also run unit tests in watch mode via
npm run test,
or single-run via
npm run test:once.
You can also test your library by installing it in another local repository you have.
To do so, first build your lib via
npm run build.
Then install it from your other repo using a relative path to the dist folder:
npm install relative/path/to/library/dist.
Publishing your library
You'll also need to rename the folder your project is in.
After you have changed the package name, you can publish it to NPM (read this link for details).
Instead of following the
Updating the package on that previous doc, here we use
Read their docs to see how to use it.
First you'll need to create a NPM account and login on your local machine.
Then you can publish your package by running
npm publish dist/.
Since your package is built on the
dist/ folder this is the one you should publish.
Be a good library maintainer
Now that you've published a library, you need to maintain it as well. Below are some of the most important points:
- Document your library.
- Keep an eye on the issue tracker.
- Manage your dependencies properly
- Follow Semantic Versioning
- Setup a Continuous Integration solution to test your library (included is a
.travis.ymlfile for Travis CI)!
- Choose an appropriate license.
Appendix: Supporting AOT
AOT plays an important role in optimizing Angular applications. It's therefore important that third party libraries be published in a format compatible with AOT compilation. Otherwise it will not be possible to include the library in an AOT compiled application.
Only code written in TypeScript can be AOT compiled.
Before publishing the library must first be compiled using the AOT compiler (
ngc extends the
tsc compiler by adding extensions to support AOT compilation in addition to
regular TypeScript compilation.
AOT compilation outputs three files that must be included in order to be compatible with AOT.
In order to preserve the original typings,
ngc will generate
.d.ts typings files.
Meta Data JSON files
ngc outputs a metadata.json file for every
These meta data files represent the information in the original
The meta data may reference external templates or css files. These external files must be included with the library.
ngc generates a series of files with an
.ngfactory suffix as well.
These files represent the AOT compiled source, but should not be included with the published library.
ngc compiler in the consuming application will generate
.ngfactory files based
Why not publish TypeScript?
Why not ship TypeScript source instead? After all the library will be part of another TypeScript compilation step when the library is imported by the consuming application.
Generally it's discouraged to ship TypeScript with third party libraries.
It would require the consumer to replicate the complete build environment of the library.
Not only typings, but potentially a specific version of
ngc as well.
Appendix: Supporting JIT
AOT compiled code is the preferred format for production builds, but due to the long compilation time it may not be practical to use AOT during development.
To create a more flexible developer experience a JIT compatible build of the library should be
published as well.
The format of the JIT bundle is
umd, which stands for Universal Module Definition.
Shipping the bundle as
umd ensures compatibility with most common module loading formats.
any external templates or css.
Appendix: Dependency Management
As a library maintainer, it's important to properly manage your dependencies in
There are three kinds of dependencies:
dependencies: here go all the other libraries yours depends on when being used. A good way to figure out these is to go through your library source code (in
src/libonly) and list all the libraries there.
devDependencies: libraries that you need while developing, testing and building your library go here. When a user installs your library, these won't be installed. Users don't need to develop, build or test your library, they just need to run it.
peerDependencies: these are similar to
dependenciessince your library expects them to be there at runtime. The difference is that you don't want to install a new version of these, but instead use the one already available.
A good example of a peer dependency is
@angular/core and all other main Angular libraries.
If you listed these in
dependencies, a new one - with a different version! - could be installed
for your library to use.
This isn't what you wanted though. You want your library to use the exact same
that the app is using.
You'll usually used
@angular/* libraries listed in both
This is normal and expected, because when you're developing your library also need a copy of
Another thing to remember is to keep your dependencies from changing too much unexpectedly. Different versions of libraries can have different features, and if you inadvertently are too lenient with allowed versions your library might stop working because a dependency changed.
You can choose what versions you allow by using ranges.
A good rule of thumb is to have all
dependencies specified with a tilde
peerDependencies have a range (
"@angular/core": ">=4.0.0 <5.0.0 || >=4.0.0-beta <5.0.0").
Any extra dependency or peer dependency that you add to
package.json should also be added
external array in the
rollupBaseConfig variable in
This ensures your library doesn't package extra libraries inside of it and instead uses the ones available in the consuming app.