duckie

duckie

A Javascript type annotation and assertion library with no dependecies. You can make it work anywhere as long as you have es5 shimed your environment.

Install

For node/browserify/webpack user, use npm install.

npm install duckie

For client user, please download the dist file in the build directory.

Example

var duckie = require('duckie');
duckie.array.test([1,2,3]) // true
duckie.array.test('123') // false
 
duckie.objectOf({
  name: String
}).test({name: 'jack'})  // true
 
duckie.arrayOf({
  name: String
}).test([{name: 'jack'}]) //true

Example

With duckie, it will ease all of your pain. Defining types is just like defining an object.

function post(data) {
  duckie.ArrayOf({
    name: String,
    age: Number
  }).assert(data); // if data doesn't fit the type, it will throw error
}

Quick Start

Intro

All the type-checker below will contain 2 functions:

• test will return a boolean to indicate if the val belongs to the type
• assert will throw an error if the val doesn't belong to the type

For example: duckie.array.test('abcd') will return false, and duckie.array.assert('abcd') will throw an error.

Basic Type

There are 8 basic types for you to directly use, they are:

• bool
• string
• number
• undefined
• null
• array
• object
• anything, means any value.

example:

duckie.bool.test(true)  => true
duckie.number.test(123) => true
duckie.array.test([1,2,3]) => true
duckie.array.test('hello') => false

Conditional Type

• oneOf(Array), any value that is one of the enums.

duckie.OneOf(['a', 'b', 'c']).test('a') // true
duckie.OneOf([1, 2, ,3]).test('a')      // false

• oneOfType([Type1, Type2..TypeN]), any value that belongs to one of the listed types.

duckie.oneOfType([String, Array]).test('abc') // true
duckie.oneOfType([String, Array]).test([]) // true
duckie.oneOfType([String, Array]).test(123) //false

• maybe(Type), any value that belongs to the type or exactly equals to undefined or NaN.

duckie.maybe(String).test('abc') //true
duckie.maybe(String).test(null)  // true
duckie.maybe(String).test(undefined) //true
duckie.maybe(String).test(1)   // false

Composite Type

• arrayOf(Type), any value that is an array and all the items in the array is type Type

duckie.arrayOf(String).test(['abc', 'bcd']) //true
duckie.arrayOf(String).test(['abc', 1])     // false, because there is a number 1 which isn't of type String
duckie.arrayOf(duckie.maybe(String)).test(['abc', null])  //true, it means array can contain string(s) or null/undefined(s)

• objectOf(/*definition*/), an object that contains the structure described with definition.

duckie.objectOf({name: String}).test({name: 'jack'})   // true
duckie.objectOf({name: String}).test({name: 'jack', age: 18}) // true, because it only check duck type
duckie.objectOf({name: String, gender: String).test({name: 'jack'}) //false, because it not contain gender
// how to describe if a field is optional? use maybe
duckie.objectOf({name: String, age: T.maybe(Number)}).test({name: 'jack'}) // true, because age is optional

Complex Type

How to desribe a data structure that:

• is an array.
• each item is a Person
• the definition of Person is: it has a name as String, age as Number and hobbies as Array of String.

Obviously, we can combine arrayOf and ObjectOf together to achieve the goal.

// first, build an array with person type
duckie.arrayOf(Person)
 
// second, investigate Person type
duckie.objectOf({
  name: String,
  age:  Number,
  hobbies: duckie.arrayOf(String)
})
 
// finally, combine them and we get
duckie.arrayOf(duckie.objectOf{
  name: String,
  age:  Number,
  hobbies: duckie.arrayOf(String)
})

Do you find it a little verbose? It looks like we are using something DSL rather than use JS. Why can't we define data structure just as defining data itself? The answer is: Yes, we can.

For arrayOf and objectOf, you don't need to wrap any type checker for inner definitions. It means:

duckie.arrayOf(duckie.objectOf({
  name: String
}))
 
is just the same as:
 
duckie.arrayOf({
  name: String
})

so the complex definition of T.arrayOf(Person) can be written as:

duckie.arrayOf({  // omitting the objectOf makes your code cleaner
  name: String,
  age:  Number,
  hobbies: [String]  // you can defined the ArrayOf(String) as [String]
})

Shortcut

For the reason we may want to defined the data structure just like defining the data itself. We can use duckie(Type) to create a type checker. For Example:

duckie([]).test([1,2,3]) // the same as duckie.array.test([1,2,3])
duckie([Number]).test([1,2,3]) // the same as duckie.arrayOf(Number).test([1,2,3])
duckie({name: String}).test({name: 'jack'})  // the same as duckie.objectOf({name: String}).test({name: 'jack'})

CAUTION: duckie([Number, String]) still means duckie.arrayOf(Number) because we tend to think all the items in the array should be the same type and expression duckie([Number, String]) doesn't make any sense.

License

MIT