NOTE: The article is relevant to the earlier versions of Angular and with the version 7 and above, we can create a library in Angular using the command ng generate library . For more on this, refer to the documentation here: https://next.angular.io/guide/creating-libraries
When you have a small application with three or more components, and they do not share a relationship among themselves when it comes to sharing data through component communication. For such components, we have seen the usage of services. Services come to be of great help when we have to use the same data in more than one components. This data is then used inside the component by using dependency injection.
This is when we have the components inside one module which contains the service. However, if we want to use the data from the service in multiple modules, a better idea is to put this data inside the service somewhere, from where you can actually import it in whichever module and component you wish to.
Now, this is about one application, what if you want maximum applications to use the same data and you definitely do not want to copy paste the code for each of your applications. Also, you do not want any of the applications to communicate with each other, but just share some data from an external source to all the applications.
That is when Libraries and packages come into the picture. In this blog post, we will see how to create an Angular library and what are the requirements to create one. When researching more about Angular libraries, I came across this great talk Create and publish Angular libs like a Pro by Juri Strumpflohner wherein he explains the need for a library with this image.
To start with, let us look at the points to consider when creating a library.
A library should be:
Supporting Ahead-of-time compilation
Work with TypeScript doing type checking, autocompletion, etc.
All these requirements together make a perfect Angular library, and it has come up with a solution called Angular Package format to support building the Angular libraries. This format is a recommended way of building Angular libraries and distributing the packages. Libraries which are built using this format will be handled properly by the Angular applications, node packages, npm.
It is a set of guidelines which Angular team uses to distribute packages and if we follow those guidelines while developing an Angular library, we put ourselves on a safe side because then our library is supported by a lot of tools that are used in the ng ecosystem and the packages then integrate easily with these tools. It will also have an optimized bundle size and a build time which are some of the very important factors.
Steps to produce an Angular library
Since the library should be bundled all in once place, the first step should be to inline all the external templates.
Build different ESM2015, UMD formats.
We can developer libraries using the ng-packagr, which is a project on nom and Github. These libraries can then be put inside the Angular Package Format. The libraries create all the bundles for us. It is consumed by different module loaders, inline the templates by itself, creates the type definitions (.d.ts files)
To install ng-packagr using npm, so that it can then be used globally from the command line,