renolc/genre

Object template declaration and runtime type checking

genre

Object template declaration and runtime type checking

Installation

npm i genre

Usage

genre is really just a simple function. It takes in an object, and a template you wish to compare it to. The function will return true or false depending on if the object matches the template.

const check = require('genre')

const template = {
  name: i => i === 'Bob'
}

check({ name: 'Bob' }, template)  // true
check({ name: 'John' }, template) // false

As the above code shows, the template is an object with functions to validate fields. In this example, the name field is being validated as equaling "Bob".

This isn't a very handy template, but it showcases how genre can be used to validate fields on objects. Most of the time you will care more about the presence of certain fields, and what types or range the values are in. For this reason, genre comes with several predefined types you may utilize as well:

const check = require('genre')
const { Str, Num, Bool } = require('genre/types')

const template = {
  name: Str,
  age: Num,
  isAdmin: Bool
}

// true
check({
  name: 'Phil',
  age: 30,
  isAdmin: true
}, template)

Types

Here is a list of all predefined types genre includes:

Name	Description
Any	any non-null value
Str	is value a String
Num	is value a Number
Bool	is value a Boolean
Int	is value an integer
Float	is value a float
Arr(T?)	is value an array of type T (T default to Any)
Obj(template?)	is value an Object (if template is provided, check value against it)
Dat	is value a Date
Fun	is value a Function
GT(n, T)	is value of type T and > n
GTE(n, T)	is value of type T and >= n
LT(n, T)	is value of type T and < n
LTE(n, T)	is value of type T and <= n
EQ(n, T)	is value of type T and == n
EQQ(n, T)	is value of type T and === n
NEQ(n, T)	is value of type T and != n
NEQQ(n, T)	is value of type T and !== n
Or(...T)	is value of any provided type
Not(...T)	is value of any type other than those provided
Enum(...values)	is value included in list of values
Optional(T)	make field optional (validates to true if null or undefined)

Advanced Types

Types can be combined to create advanced types for use in templates:

const Between0And100 = GTE(0, LTE(100, Int))

const Documents = Arr(Obj({
  title: Str,
  content: Str
}))

const ArrayOfIntsOrStrings = Arr(Or(Int, Str))

const OptionalArrayOfNonEmptyStrings = Optional(Arr(NEQ(false, Str)))

By default, if any field defined on the template is missing from the object, the check will fail. Utilize Optional to define fields as being not required.

Once again, the types are really just functions that take in a value and return true or false if they should pass. Feel free to create your own validation functions to use and abuse as you see fit:

const template = {
  // only even ages... for reasons
  age: i => i % 2 === 0,

  // check against list of allowed names
  name: i => ['Phil', 'Amanda', 'Chris'].includes(i),

  // flip of the coin -- not recommended
  isAdmin: () => Math.random() > 0.5
}