There are many things that have changed in version 2 of the ASP.NET Coreframework. There have been a lot of improvements in some of its supporting technologies as well. Now is a great time to give it a try, as its code has been stabilized and the pace of change has settled down a bit.

There were significant differences between the original release candidate and version 1 of ASP.NET Core and further alterations between version 1 and version 2. Some of these changes have been controversial, particularly ones related to tooling; however, the scope of .NET Core has grown massively, and this is a good thing.

One of the high-profile differences between version 1 and version 2 is the change (some would say regression) from the new JavaScript Object Notation (JSON)-based project format back to the Extensible Markup Language (XML)-based csproj format. However, it is a simplified and stripped-down version, compared to the format used in the original .NET Framework.

There has been a move toward standardization between the different .NET Frameworks, and .NET Core 2 has a much larger API surface as a result. The interface specification, known as .NET Standard 2, covers the intersection between .NET Core, the .NET Framework, and Xamarin. There is also an effort to standardize Extensible Application Markup Language (XAML) into the XAML standard, which will work across Universal Windows Platform (UWP) and Xamarin.Forms apps.

C# and .NET can be used on a huge range of diverse platforms and in a large number of different use cases, from server-side web applications to mobile apps and even games (using game engines such as Unity 3D). In this book, we'll focus on web application programming and, in particular, on general ways to make web apps perform well. This means that we will also cover client-side web browser scripting with JavaScript and the performance implications involved.

This book is not just about C# and ASP.NET. It takes a holistic approach to performance and aims to educate you about a wide range of relevant topics. We don't have the space to take a deep dive into everything, so the idea here is to help you discover some useful tools, technologies, and techniques.

In this chapter, we will go through the changes between version 1 and version 2 of both .NET Core and ASP.NET Core. We will also look at some new features of the C# language. There have been many useful additions and a plethora of performance improvements too.

In this chapter, we will cover the following topics: