Important and Most Used:

1. compilerOptions:

   • This section contains various options for controlling TypeScript compilation.
     • target: Specifies the ECMAScript target version (e.g., ES5, ES6, etc.).
     • module: Specifies the module system (e.g., CommonJS, ES6, etc.).
     • strict: Enables strict type checking options.
     • esModuleInterop: Ensures compatibility between CommonJS and ES module imports.

2. include:

   • An array of file or directory patterns to include in the compilation process. Usually, this contains your TypeScript code.

3. exclude:

   • An array of file or directory patterns to exclude from the compilation. Commonly, this includes folders like node_modules.

4. extends:

   • Allows one tsconfig.json file to extend another. This is useful for sharing settings across multiple projects.

Less Common but Still Important:

5. compilerOptions.lib:

   • Specifies the libraries that should be available at runtime. It's often set to "dom" for browser-related projects.

6. compilerOptions.types:

   • Specifies the types that should be available for TypeScript to reference. This is useful for including external type definitions.

7. compilerOptions.outDir:

   • Specifies the output directory for compiled files.

8. compilerOptions.rootDir:

   • Sets the root directory of input files. TypeScript uses this to determine the original location of files for maintaining the directory structure in the output.

Less Common and More Specialized:

9. compilerOptions.paths:

   • Allows you to specify module name mappings to different directories. Useful for module resolution and aliases.

10. compilerOptions.noEmit:

    • Instructs TypeScript not to emit any output. This can be useful for projects that only need type checking.

11. compilerOptions.declaration:

    • Generates corresponding .d.ts files for your TypeScript files. This is important when creating libraries or packages.

12. compilerOptions.sourceMap:

    • Generates source maps which can be useful for debugging TypeScript code in the browser.

13. compilerOptions.allowJs:

    • Enables TypeScript to process JavaScript files.

Less Common and Niche Use Cases:

14. compilerOptions.noImplicitAny:

    • Flags an error if a variable has an implicit any type.

15. compilerOptions.experimentalDecorators:

    • Enables support for experimental ECMAScript decorators.

16. compilerOptions.noUnusedLocals / noUnusedParameters:

    • Flags unused local variables or parameters.

17. compilerOptions.forceConsistentCasingInFileNames:

    • Ensures that file paths are consistently cased.

18. compilerOptions.incremental:

    • Enables incremental compilation which can improve build times.

19. compilerOptions.importHelpers:

    • Allows the import of helper functions from tslib.

20. compilerOptions.baseUrl / paths:

    • Used for module resolution and aliases.

21. compilerOptions.strictNullChecks:

    • Enables strict null checks, which helps catch common programming mistakes related to null and undefined.

22. compilerOptions.noImplicitThis:

    • Flags an error when this is used in a context where it is assumed to have a certain type.

23. compilerOptions.alwaysStrict:

    • Enables strict mode semantics in all files.

24. compilerOptions.noFallthroughCasesInSwitch:

    • Flags an error for fallthrough cases in switch statements.