[javascript] How to describe "object" arguments in jsdoc?

// My function does X and Y.
// @params {object} parameters An object containing the parameters
// @params {function} callback The callback function
function(parameters, callback) {
}

But how do I describe how the parameters object should be structured? For example it should be something like:

{
  setting1 : 123, // (required, integer)
  setting2 : 'asdf' // (optional, string)
}

I see that there is already an answer about the @return tag, but I want to give more details about it.

First of all, the official JSDoc 3 documentation doesn't give us any examples about the @return for a custom object. Please see https://jsdoc.app/tags-returns.html. Now, let's see what we can do until some standard will appear.

• Function returns object where keys are dynamically generated. Example: {1: 'Pete', 2: 'Mary', 3: 'John'}. Usually, we iterate over this object with the help of for(var key in obj){...}.

  Possible JSDoc according to https://google.github.io/styleguide/javascriptguide.xml#JsTypes

  /**
   * @return {Object.<number, string>}
   */
  function getTmpObject() {
      var result = {}
      for (var i = 10; i >= 0; i--) {
          result[i * 3] = 'someValue' + i;
      }
      return result
  }
  

• Function returns object where keys are known constants. Example: {id: 1, title: 'Hello world', type: 'LEARN', children: {...}}. We can easily access properties of this object: object.id.

  Possible JSDoc according to https://groups.google.com/forum/#!topic/jsdoc-users/TMvUedK9tC4

  • Fake It.

    /**
     * Generate a point.
     *
     * @returns {Object} point - The point generated by the factory.
     * @returns {number} point.x - The x coordinate.
     * @returns {number} point.y - The y coordinate.
     */
    var pointFactory = function (x, y) {
        return {
            x:x,
            y:y
        }
    }
    

  • The Full Monty.

    /**
     @class generatedPoint
     @private
     @type {Object}
     @property {number} x The x coordinate.
     @property {number} y The y coordinate.
     */
    function generatedPoint(x, y) {
        return {
            x:x,
            y:y
        };
    }
    
    /**
     * Generate a point.
     *
     * @returns {generatedPoint} The point generated by the factory.
     */
    
    var pointFactory = function (x, y) {
        return new generatedPoint(x, y);
    }
    

  • Define a type.

    /**
     @typedef generatedPoint
     @type {Object}
     @property {number} x The x coordinate.
     @property {number} y The y coordinate.
     */
    
    
    /**
     * Generate a point.
     *
     * @returns {generatedPoint} The point generated by the factory.
     */
    
    var pointFactory = function (x, y) {
        return {
            x:x,
            y:y
        }
    }
    

  According to https://google.github.io/styleguide/javascriptguide.xml#JsTypes

  • The record type.

    /**
     * @return {{myNum: number, myObject}}
     * An anonymous type with the given type members.
     */
    function getTmpObject() {
        return {
            myNum: 2,
            myObject: 0 || undefined || {}
        }
    }
    

By now there are 4 different ways to document objects as parameters/types. Each has its own uses. Only 3 of them can be used to document return values, though.

For objects with a known set of properties (Variant A)

/**
 * @param {{a: number, b: string, c}} myObj description
 */

This syntax is ideal for objects that are used only as parameters for this function and don't require further description of each property. It can be used for @returns as well.

For objects with a known set of properties (Variant B)

Very useful is the parameters with properties syntax:

/**
 * @param {Object} myObj description
 * @param {number} myObj.a description
 * @param {string} myObj.b description
 * @param {} myObj.c description
 */

This syntax is ideal for objects that are used only as parameters for this function and that require further description of each property. This can not be used for @returns.

For objects that will be used at more than one point in source

In this case a @typedef comes in very handy. You can define the type at one point in your source and use it as a type for @param or @returns or other JSDoc tags that can make use of a type.

/**
 * @typedef {Object} Person
 * @property {string} name how the person is called
 * @property {number} age how many years the person lived
 */

You can then use this in a @param tag:

/**
 * @param {Person} p - Description of p
 */

Or in a @returns:

/**
 * @returns {Person} Description
 */

For objects whose values are all the same type

/**
 * @param {Object.<string, number>} dict
 */

The first type (string) documents the type of the keys which in JavaScript is always a string or at least will always be coerced to a string. The second type (number) is the type of the value; this can be any type. This syntax can be used for @returns as well.

Resources

Useful information about documenting types can be found here:

https://jsdoc.app/tags-type.html

PS:

to document an optional value you can use []:

/**
 * @param {number} [opt_number] this number is optional
 */

or:

/**
 * @param {number|undefined} opt_number this number is optional
 */

For @return tag use {{field1: Number, field2: String}}, see: http://wiki.servoy.com/display/public/DOCS/Annotating+JavaScript+using+JSDoc

There's a new @config tag for these cases. They link to the preceding @param.

/** My function does X and Y.
    @params {object} parameters An object containing the parameters
    @config {integer} setting1 A required setting.
    @config {string} [setting2] An optional setting.
    @params {MyClass~FuncCallback} callback The callback function
*/
function(parameters, callback) {
    // ...
};

/**
 * This callback is displayed as part of the MyClass class.
 * @callback MyClass~FuncCallback
 * @param {number} responseCode
 * @param {string} responseMessage
 */

If a parameter is expected to have a specific property, you can document that property by providing an additional @param tag. For example, if an employee parameter is expected to have name and department properties, you can document it as follows:

/**
 * Assign the project to a list of employees.
 * @param {Object[]} employees - The employees who are responsible for the project.
 * @param {string} employees[].name - The name of an employee.
 * @param {string} employees[].department - The employee's department.
 */
function(employees) {
    // ...
}

If a parameter is destructured without an explicit name, you can give the object an appropriate one and document its properties.

/**
 * Assign the project to an employee.
 * @param {Object} employee - The employee who is responsible for the project.
 * @param {string} employee.name - The name of the employee.
 * @param {string} employee.department - The employee's department.
 */
Project.prototype.assign = function({ name, department }) {
    // ...
};

Source: JSDoc