Extract inferred return types from functions that are exported in TypeScript file

main.ts

import fs = require('fs');
import ts = require('typescript');

// Create the language service host to allow the LS to communicate with the host
const servicesHost: ts.LanguageServiceHost = {
	getScriptFileNames: () => rootFileNames,
	getScriptVersion: (fileName) => files[fileName] && files[fileName].version.toString(),
	getScriptSnapshot: (fileName) => {
		if (!fs.existsSync(fileName)) {
			return undefined;
		}

		return ts.ScriptSnapshot.fromString(fs.readFileSync(fileName).toString());
	},
	getCurrentDirectory: () => process.cwd(),
	getCompilationSettings: () => ({
		target: ts.ScriptTarget.ES2016,
		skipDefaultLibCheck: true,
		lib: ['lib.es6.d.ts', 'lib.scripthost.d.ts'],
		removeComments: true
	}),
	getDefaultLibFileName: (options) => ts.getDefaultLibFilePath(options),
	fileExists: ts.sys.fileExists,
	readFile: ts.sys.readFile,
	readDirectory: ts.sys.readDirectory,
};

const rootFileNames: string[] = [];
const files: { [k: string]: { version: number } } = {};

// Create the language service files
const services = ts.createLanguageService(
	servicesHost,
	ts.createDocumentRegistry()
);

const fileName = 'test.ts';

rootFileNames.push(fileName);
files[fileName] = {
	version: 0
};

const program = services.getProgram();
const typeChecker = program.getTypeChecker();
const sourceFile = program.getSourceFile(fileName);
ts.isFunctionDeclaration
sourceFile.statements.forEach((statement) => {
	const f = statement as ts.FunctionDeclaration
	console.log(
		f.name!.escapedText,
		typeChecker.typeToString(typeChecker.getTypeAtLocation(f.type!)),
		typeChecker.typeToString(typeChecker.getReturnTypeOfSignature(typeChecker.getSignatureFromDeclaration(f))),
		// typeChecker.typeToString(),
	);
});

test.ts

export function aFunction() {
	return 'Obviously a string';
}

export function bFunction() {
	return ['Obviously a string'];
}