How to get `CompilerOptions` from `tsconfig.json`

Question

I'm working with the TypeScript compiler API. When initializing a program, I'm asked to supply a CompilerOptions object. I want to use the CompilerOptions for a given tsconfig.json file, but I can't seem to figure out what the right way is to get this.

I think I'm supposed to use parseJsonConfigFileContent but that also needs a ParseConfigHost. They say that it's easy to implement yourself, but particularly the method readDirectory seems rather complicated to implement yourself. As far as I can see, you need to return all TypeScript files in a certain directory, accounting for a excludes and includes.

Surely, TypeScript does this internally somewhere already. How can I use the default readDirectory or ParseConfigHost?

Phrased in another way: what's the simplest way to get the CompilerOptions for a given TypeScript project?

Answer 1

With the following code I was able to easily read the compiler options.

I don't yet know if this has any limitations, but it seems to work fine and it only uses things that Typescript itself provides:

const configFileName = ts.findConfigFile(
  "./",
  ts.sys.fileExists,
  "tsconfig.json"
);
const configFile = ts.readConfigFile(configFileName, ts.sys.readFile);
const compilerOptions = ts.parseJsonConfigFileContent(
  configFile.config,
  ts.sys,
  "./"
);