> Why even use else if with return...

What is the problem with that? How would you write that snippet? It is common in the new functional js landscape, even if it is pass-by-ref.

Using guard clauses. Way more readable and easy to work with.

  export function extractSearchToken(completionToken: {
    token: string;
    isQuoted?: boolean;
  }): string {
    if (completionToken.isQuoted) {
      return completionToken.token.slice(2).replace(/"$/, '');
    }
    if (completionToken.token.startsWith('@')) {
      return completionToken.token.substring(1);
    }
    return completionToken.token;
  }