The tsconfig.json file is the TypeScript configuration file. Again, those who already know what TypeScript is won't need to read all this, although the others should most likely stay.

In less than 100 words, TypeScript is a free, open source programming language developed and maintained by Microsoft that acts as a JavaScript superset; this means that any JavaScript program is also a valid TypeScript program. TypeScript also compiles to JavaScript, so it can seamlessly work on any JS-compatible browser without external components. The main reason to use it is to overcome the syntax limitations and overall shortcomings of JavaScript when developing large-scale applications or complex projects: in very short terms, to ease the developer's life when he's forced to deal with non-trivial JavaScript code.

In this project, we will definitely use TypeScript for a number of good reasons; the most important ones of them are as follows:

• TypeScript has a number of features over JavaScript, such as static typing, classes, and interfaces. Using it in Visual Studio also gives us the chance to benefit from the built-in IntelliSense, which is a great benefit and often leads to a remarkable productivity burst.
• For a large client-side project, TypeScript will allow us to produce a more robust code, which will also be fully deployable anywhere a plain JavaScript file would run.

Not to mention the fact that the Angular SPA template we chose is using it, hence we can say that we got a leg in that boat already!

Jokes aside, we're not the only ones praising TypeScript; it's something acknowledged by the Angular team itself, considering the fact that the Angular source code has been written using TypeScript since Angular 2, as proudly announced by Microsoft in the following MDSN blog post in March 2015:

https://blogs.msdn.microsoft.com/typescript/2015/03/05/angular-2-built-on-typescript/

It was further emphasized by this great post by Victor Savkin (co-founder of Narwhal Technologies and acknowledged Angular consultant) on his personal blog in October 2016:

Getting back to the tsconfig.json file, there's not much to say; the option values used by the Angular SPA Template are more or less what we need to configure both Visual Studio and TSC (the TypeScript compiler) to properly transpile the TS code files included in the /ClientApp/ folder: however, while we're here, we can take the chance to tweak them a little more:

{
  "compilerOptions": {
    "module": "es2015",
    "moduleResolution": "node",
    "target": "es5",
    "sourceMap": true,
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true,
    "skipDefaultLibCheck": true,
    "skipLibCheck": true,
    "strict": true,
    "lib": [ "es6", "dom" ],
    "types": [ "webpack-env" ]
  },
  "exclude": [ "bin", "node_modules" ],
  "atom": { "rewriteTsconfig": false },
  "angularCompilerOptions": {
    "strictMetadataEmit": true
  }
}

The interesting stuff here is the angularCompilerOptions object, which can be used to configure the behavior of the Angular AoT compiler: the strictMetadataEmit setting which we added will tell the compiler to report syntax errors immediately rather than produce an error log file.