‘await’ has no effect on the type of this expression

I was getting this error just because my JSDoc comment was incorrect.

For example I had an async function that had @returns {string}:

  /**
   * Fetch from the swapi API
   *
   * @param {string} type
   * @param {string} id
   * @returns {string} JSON
   */
  export default async (type, id) => {
    console.table([ type, id ]);
    const response = await fetch(`https://swapi.co/api/${type}/?page=${id}`);
    const json = await response.json();
    console.log(json);
    return json;
  }

I was getting the “‘await’ has no effect on the type of this expression” warning – but the function looked correct.

However once I changed the JSDoc to @returns {Promise<string>} then the error disappeared:

  /**
   * Fetch from the swapi API
   *
   * @param {string} type
   * @param {string} id
   * @returns {Promise<string>} JSON
   */

You can also use the @async hint as the JSDoc documentation suggests:

/**
 * Download data from the specified URL.
 *
 * @async
 * @function downloadData
 * @param {string} url - The URL to download from.
 * @returns {Promise<string>} The data from the URL.
 */