JSDoc for class method, overloading, adding multiple signatures.

jsdoc-class-method-overload.js

/**
 * @typedef {(x: number) => string} NumberToStringType
 * 
 * @typedef {(x: string) => number} StringToNumberType
 * 
 * @typedef {NumberToStringType & StringToNumberType} FlipType
 */

class SampleClass {
  constructor() {
    /**
     * @type {FlipType}
     */
    this.flip = this._flip;
  }

  /**
   * @type {FlipType}
   * The @type definition will not effect here
   */
  _flip(x) {
    if (typeof x === 'string')
      return Number(x);
    else
      return String(x);
  }
}

let sample = new SampleClass();

let number1 = sample.flip(1); // string
let string1 = sample.flip("1"); // number

let number2 = sample._flip(2); // string | number
let string2 = sample._flip("2"); // string | number

/**
 * Arrow function
 * 
 * @type {FlipType}
 */
const flipper = x => {
  if (typeof x === 'string')
    return Number(x);
  else
    return String(x);
}

let number3 = flipper(3); // string
let string3 = flipper("3"); // number

It would be nice to hae this feature working without hacking the class prototype....