type annotation DSL

npm install deftypes
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JavaScript type annotaion DSL library for structure and function.

Provide simple DSL and No side effects

It is type checker on execution(not static).

Deftypes can avoid all side effects if you want. It may be also good on testing framework.


Examples are coffee-script.


$ npm install deftypes
{def, defun, T} = require 'deftypes'


$ bower install deftypes
<script src="bower_components/deftypes/deftypes.js"></script>

or download deftypes.js of this directory

<script src="master/deftypes.js"></script>

It provides DSLs => def, defun, T

How to use

Struct Definition

Point = {x: Number, y: Number}
p1 = def Point, {x:1, y:2} #=> {x: 1, y:2}
p2 = def Point, {x:1, z:2} #=> type error

Typed Array

list = def [T.Int], [1,2,3]

(T.Int and T.Fload are defined by default)


NullableNumber = {n: T.Nullable(Number)}
p1 = def NullableNumber, n:1
p2 = def NullableNumber, n:null

Typed Hash

id_table = def T.Hash(String, Number), {

Key accepts only Number or String (but it doesn't check yet)

Function Definition

check arguments and returned object

f1 = def T.Func([Number, Number], String), (m, n) -> "#{m}, #{n}"
f1(1,2) #=> "1, 2"
f1("",2) #=> argument error
find_index = def T.Func([[Number], Number], T.Nullable(Number)), (arr, n) ->
  if (index = arr.indexOf(n)) is -1 then null else index

find_index([3,4,5], 4) #=> 1
find_index([3,4,5], 9) #=> null

Function DSL

f2 = defun [Number, Number], String, (m, n) -> "#{m}, #{n}"

Any Type

events = def Object, require('events')
list = def [T.any], [0, "", null]

Function Scope with type check

p = def Point, {x:1, y:2}
def Point, p, ->
  @x = 3

# Type Error
def Point, p, -> @y = "not number"

Transparent mode

if option.transparent is true, typechecker does nothing, passing through def like transparent for avoiding performance down.

{option} = require 'deftypes'
option.transparent = true
Deftypes.option.transparent = true


  • trait feature
  • struct inheritance
  • valid error message
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