printer.printFile prints empty string

Question

I am using the compiler API to create Typescript code. After assigning const printer = createPrinter(), I can use printer.printNode and printer.printList to print my AST. But for some reason, printer.printFile always prints empty strings.

const printer = createPrinter();
    
const sourceFile = createSourceFile(
  'dummy.ts',
  '',
  ScriptTarget.ESNext,
  false,
  ScriptKind.TS
);

const classDeclaration = factory.createClassDeclaration(
  undefined,
  undefined,
  'Foo',
  undefined,
  undefined,
  []
);

factory.updateSourceFile(sourceFile, factory.createNodeArray([classDeclaration]));

console.log(printer.printFile(sourceFile)); // '';

Why is printer.printFile always printing an empty string?

Answer 1

I'm not sure why but it looks like the factory.updateSourceFile returns the updated SourceFile.

const printer = createPrinter();
   
// const -> let 
let sourceFile = createSourceFile(
  'dummy.ts',
  '',
  ScriptTarget.ESNext,
  false,
  ScriptKind.TS
);

const classDeclaration = factory.createClassDeclaration(
  undefined,
  undefined,
  'Foo',
  undefined,
  undefined,
  []
);

// assign the updated source file
sourceFile = factory.updateSourceFile(sourceFile, factory.createNodeArray([classDeclaration]));

console.log(printer.printFile(sourceFile));
// class Foo {
// }