Two players, one goal

From the perspective of a fully-functional web-based application, we can say that the web API interface provided with the ASP.NET Core framework is a programmatic set of server-side handlers used by the server to expose a number of hooks and/or endpoints to a defined request-response message system, typically expressed in structured markup languages, such as JSON or XML. As we already said, this is achieved by making good use of the HTTP protocol handled by a publicly-available web server (typically IIS). Similarly, Angular can be described as a modern, feature-rich client-side library that pushes the HTML5 features--along with the modern browser's capabilities--to their full extent by binding the input and/or output parts of an HTML web page into a flexible, reusable, and easily testable JavaScript model.

These assumptions allow us to answer to a simple, yet inevitable question "can we combine the backend strengths of ASP.NET Core's web API with the frontend capabilities of the Angular framework in order to build a modern, feature-rich, and highly versatile web application?

The answer, in short terms, is yes. In the following chapters, we'll see how we can do that by analyzing all the fundamental aspects of a well-written, properly designed web-based product, and how ASP.NET Core and/or Angular can be used to handle each one of them.

The ASP.NET core revolution

To summarize what happened in the ASP.NET world within the last two years is not an easy task; in short words, we can say that we're undoubtedly facing the most important series of changes in the .NET Framework since the year it came to life. ASP.NET Core 1.0, which came out in Q3 2016, was a complete re-implementation of the ASP.NET we knew; the brand new framework unites all the previous web application technologies, such as MVC, Web API, and web pages, into a single programming module, formerly known as MVC6. The new framework introduces a fully-featured cross-platform component, also known as .NET Core, shipped with a brand new open source .NET Compiler Platform (currently known as Roslyn), a cross-platform runtime (known as CoreCLR), and an improved x64 Just-In-Time compiler (RyuJIT).

The 1.0 final release was shortly followed by ASP.NET Core 1.1 (Q4 2016), which brought some new features and performance enhancements, and also addressed many bugs and compatibility issues affecting the former one.

The third and, at the time of writing, the latest step was taken with ASP.NET Core 2.0, which came out in Q2 2017 as a preview and then in Q3 2017 for the final release; the newer version features among a number of significant improvements with a huge effort to standardize the shared APIs among the .NET Framework, .NET Core, and Xamarin, making it easy for developers to share and reuse code across the whole .NET ecosystem.

Someone might be wondering about what happened to ASP.NET 5 and Web API 2, as these used to be quite popular names until mid-2016.
ASP.NET 5 was no less than the original name of ASP.NET Core, before the developers chose to rename it to emphasize the fact that it is a complete rewrite. The reasons for that, along with the Microsoft vision about the new product, are further explained in the following Scott Hanselman's blog post that anticipated the changes on Jan 16, 2016:
http://www.hanselman.com/blog/ASPNET5IsDeadIntroducingASPNETCore10AndNETCore10.aspx
For those who don't know, Scott Hanselman is the outreach and community manager for .NET/ASP.NET/IIS/Azure and Visual Studio since 2007.
Additional information regarding the perspective switch is also available in the following article by Jeffrey T. Fritz, Program Manager for Microsoft and NuGet team leader:
https://blogs.msdn.microsoft.com/webdev/2016/02/01/an-update-on-asp-net-core-and-net-core/
As for Web API 2, it was a dedicated framework for building HTTP services returning pure JSON or XML data instead of web pages. Initially born as an alternative to the MVC platform, it has been merged with the latter into the new, general-purpose web application framework known as MVC6, which is now shipped as a separate module of ASP.NET Core.

What's new in Angular?

The new release of AngularJS, simply known as Angular, is a complete rewrite of the previous one, entirely based upon TypeScript and ECMAScript 6 specifications.

If you're a seasoned web developer, most likely, you already know what TypeScript is. In case you don't, no worries, we'll get to that later on.

The choice of not making Angular backward compatible with AngularJS clearly demonstrates the intention of the author's team to adopt a completely new approach--any developer who already knows AngularJS will undoubtedly face a huge number of breaking changes, not only in the code syntax, but also in the way of thinking and designing the client app. Angular is highly modular, component-based, comes with a new and improved dependency injection model and a whole lot of programming patterns its older cousin never heard of.

However, the most important reason we're picking Angular over other excellent JS libraries such as ReactJS and EmberJS is the fact that it already comes out with a huge pack of features out of the box, making it most suited, although maybe not as simple to use than the aforementioned competitors; if we combine that with the consistency given by the TypeScript language, we can say that despite being the youngster, Angular embraced the framework approach more convincingly than the others. This has been confirmed over the course of the past 9 to 12 months, where the project hit two major versions (Angular 2 in Q3 2016 and Angular 4 in Q1 2017), gaining a lot in terms of stability, performances, and features, without losing much in terms of backward compatibility, best practices, and overall approach. All these reasons are solid enough to invest in it, hoping it will continue to keep up with these compelling premises.