0.2.3 • Public • Published


V: 0.2.3

is a library for defensive programming through javascript ducktype checking. The idea is to check the strictly minimum requirements for a set of values. It can be used as:

  • aa.A: a comprenhesive validator (return an object whose keys are the invalid values, and their value the name of the error). When used in primitive values it will return undefined if there is no error.
  • aa.B: a boolean compliance checker (return true if the conditions are met and false otherwise). This is simply a convenience wraper for aa.a.
  • aa.E: as a super anal type asserter which will throw a type error if the conditions aren't met. As expected, the anal way allows chaining.


bower install aassert


Primitives (Out of the box types)

The primitive types supported by aassert are: number, boolean, string, array, object, function and undefined. null is treated as undefined

These primitives have the following shorthand names:

number: n
boolean: b
string: s
array: a
object: o
function: f
undefined: u

To check if a value value is a of type number just call aa.B.number(value) if you are on the keystroke saving hype just call aa.B.n(value). It will return the boolean value false if there value is not valid.

All calls to aa.E are chainable, so you can perform aa.E.n(myNumber).s(myString)..., this is particularly useful when dealing with a parameter list.

Design choices

  • NanN is not a number, even though typeof(NaN) returns number.
  • null is not an object, even though typeof(null) returns object.
  • null is considered undefined.
  • An array is an object and an array.

Custom types

To define your own types using the primitives as building blocks simply use de aa.define passing a JSON object like this:

aa.define( "dog", {
	breed: "string",
	age: "number",
	name: "string",
	tricks: "array"

from there you can simply do: aa.A.dog(myDog), aa.B.dog(myDog) and `aa.E.dog(myDog)``. All three methods are created on the run.

Of course you can reuse type definitions in other types:

aa.define( "petOwner", {
	pet: "dog",
	name: "string",
	phone: "number"

And, as expected if pet is not a complying dog aa.B.petOwner(petOwner) will return false and aa.E.petOwner(petOwner) will throw a type exception.

Or create nested types:

class: {
	teacher: {
		id: "number",
		name: "string"
	id: "number"

You can also keep the type definitions in a JSON file, and import them as follows:

aa.import(filePath, callback);

Ad-hoc types

If there's a type that will only be used once, maybe defining a global type is way too much. For those cases the aa.A.c(object, typeDescriptor), aa.B.c(object, typeDescriptor) and aa.E.c(object, typeDescriptor) methods are available. For example:

aa.B.c({name: "name",
	nested: {name: "nested_name",
		superNested: {age:3}}},

	superNested: {age: "number"}}})

will return true.

Circular dependencies(Not yet implemented)

aassert will allow circular dependencies. Say for example:

dog: {
	owner: "petOwner"


	pet: "dog"

are valid type definitions that won't fail.

Work to be done

  • Allow circular dependencies. It should work like this:

    class:{ teacher: "teacher", id: "number" } teacher: { id: "number", name: "string" }



  • Moved inside aa the calls so only one object is exposed to global namespace.
  • The old aa calls are now boolean calls that are accessible as aa.B.
  • The new new assertion mode aa.A. will return a detailed description of the type mismatches if any.
  • The old strict calls AA. are now aa.E. calls, as they throw an __E__xception.

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