Declaration files
A declaration file is a special type of file used by the TypeScript compiler. It is only used during the compilation step and is used as a sort of reference file to describe JavaScript. Declaration files are similar to the header files used in C or C++ or the interfaces used in Java. They simply describe the structure of available functions and properties but do not provide an implementation. In this section of the chapter, we will take a look at these declaration files, what they are, and how to write them.
Global variables
Most modern websites use some sort of server engine to generate the HTML pages that we use. If you are familiar with the Microsoft stack of technologies, then you will know that ASP.NET MVC is a very popular server-side rendering engine. If you are a Node developer, then you may be using one of the popular Node packages to help construct web pages through templates, such as Jade, Handlebars, or Embedded JavaScript (EJS).
Within these...