iterator-return-method.js

function readLinesSync (fileName) {
  // Dummy
  const file = {
    fileName,
    isAtEndOfFile: () => false,
    close: () => 'Closed'
  };
  
  return {
    [Symbol.iterator] () {
      return this;
    },
    next () {
      if (file.isAtEndOfFile()) {
        file.close();
        return { done: true };
      } else {
        return { value: 'foo' };
      }
    },
    // Seems to never get called?
    return () {
      console.log(file.close()); // Never gets logged
      return { done: true };
    }
  };
}

for (const line of readLinesSync('foo.txt')) {
    console.log(line); // 'foo'
    break; // Shouldn’t this automatically call the iterator’s `return` method and log 'Closed'?
}