```ts
/**
 * Returns the longest word in a sentence.
 * If two words are equally long, the first one wins.
 * An empty sentence returns an empty string.
 *
 * @param sentence - The sentence to analyze.
 * @returns The longest word or an empty string if no words are present.
 */
export function longWord(sentence: string): string {
  const words = sentence.split(/\s+/);
  let longestWord = '';

  for (const word of words) {
    if (word.length > longestWord.length) {
      longestWord = word;
    }
  }

  return longestWord;
}
```