What does `function(*=)` imply in a JSDoc-style code comment?

Question

I'm writing some code comments using JSDoc style, and want to know what *= implies in @returns {function(*=): *}, which is generated by WebStorm.

I have tried to search the JSDoc wiki and usejsdoc.org but with no result.

Below is my code:

/**
 * Get record data listener generator.
 * @param {Function} createProps
 * @returns {function(*=): *}        // ** generated by webstorm **
 */
export function getRecordCustomDataListener(createProps) {
  return (callback) => onRecordCustomData({ createRecordData: createProps })(callback); // `onRecordCustomData` has not default argument
}

I want to know what *= implies in @returns {function(*=): *}.

Answer 1

See edit at the bottom!!

Testing it in WebStorm with a small snippet seems to indicate that *= means a parameter is not optional and can be of any type where * indicates that the parameter is of any type and optional. See the following example with generated jsdoc from WebStorm:

/**
 *
 * @param createProps
 * @returns {function(*=, *): void}
 */
export function a(createProps) {
    return (callback, callback2) => console.log(callback);
}

As you can see we are only using the first parameter callback and leave callback2 unused. Webstorm generates the proper jsdoc for that.

The full jsdoc for our example above in english words: Return an arrow function that takes two parameters, a **not** optional first parameter that can be of any type, and an optional second parameter that can be of any type. That function returns void

Docs reference:

http://usejsdoc.org/tags-type.html

Optional parameter

An optional parameter named foo.

@param {number} [foo]

// or:

@param {number=} foo

An optional parameter foo with default value 1.

@param {number} [foo=1]

---

EDIT: The docs indicate that = means optional parameter but webstorm generates it with the opposite meaning. Either its wrongly documented or WebStorm does it wrong. I have tested it in WebStorm 2018.1 Build #WS-181.4203.535, built on March 22, 2018