Tutorial: 2.2 Type Operators

2.2 Type Operators

In the previous Tutorial we looked at how to write an assertion. However, you may have noticed that there is a small problem with the basic definition of an assertion: It assumes all arguments and expected values are strings. This is where type operators come in.

The Operators

There are currently 5 type operators: :string for Strings, :int for integer values, :number for float values, :bool for Booleans, and :array for Arrays.

Type Operator
String :string
Integer :int
Float :number
Boolean :bool
Array :array

To use a type operator, put it immediately after an argument or expected value. For example, if I had the assertion 2,3=>5 where 2, 3, and 5 are numbers and 5 is the sum of 2 and 3. By default, assertivedocs will read these values as strings, meaning that the sum of 2 and 3 will return 23 - a concatenation - rather than the intended 5, meaning the assertion is false. We can use :number or :int to tell assertivedocs that these are numbers: 2:int,3:int=>5:int. This assertion will now resolve as true.



By default, assertivedocs assumes all arguments and expected values are strings, however it is still good practice to include the :string operator to make it clear what you mean. Self-documenting code, even in documentation, is very useful.

 * Concatenates two words.
 * @param {String} wordA - The first word
 * @param {String} wordB - The second word
 * @returns {String}
 * @assert ConcatTest1 - Hello:string,World:string=>HelloWorld:string
function concat(wordA, wordB) {
  return wordA + wordB;

:int and :number

Vanilla JavaScript does not have an Integer type, so for all intents and purposes, :int and :number are the same operator. However, any value tagged with the :int operator will be converted to an integer, so they are not interchangeable.

 * Does the + form of the quadratic equation.
 * @param {Number} a
 * @param {Number} b
 * @param {Number} c
 * @returns {Number}
 * @assert QuadTest1 - 2:int,3:int,-4:int=>0.8507810593582121:number
function quadEquationPlus(a, b, c) {
  return (-b + (b**2 - 4*a*c)**0.5)/(2*a);


A boolean value is either true or false, but can also be 1 or 0. The :bool operator reflects this, allowing you to tag true, false, 1, or 0 as a boolean.

 * Performs the && operator on two values.
 * @param {Boolean} operandA
 * @param {Boolean} operandB
 * @returns {Boolean}
 * @assert AndTest1 - true:bool,false:bool=>false:bool
function and(operandA, operandB) {
  return operandA && operandB


:array works slightly differently to the other operators. assertivedocs works by splitting assertions first on equals greater than '=>', then on comma ',', and finally on colon ':'. This poses a problem for arrays, as they use commas as element separators by default. Therefore, in assertivedocs assertions, you define arrays using semicolons ';' as the element separator. Other than that, the definition of the array is the same: assertivedocs replaces all the semicolons with commas and then uses JSON.parse() to convert the string into an Array.

 * Outputs all the elements of an array to the console.
 * @param {any[]} array - The array
 * @returns {String}
 * @assert ListTest1 - ["Hello";"World";1;2;3]:array=>Complete:string
function listAll(array) {
  array.forEach((element) => {
  return "Complete"


In this Tutorial, we looked at how to convert the values used to create an assertion into different types.

The next Tutorial covers how assertivedocs handles undefined, null, and NaN.