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duck-check

A minimalist runtime type checking utility for duck typing

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duck-check

🦆 A minimalist runtime type checking utility.

npm version Open Source Love

New in v2.0.0

  • Remove Error batching to improve efficiency.
  • Remove complex error messages thrown by assert to improve efficiency.

Usage:

Installation

duck-check is a Javascript package published in the NPM registry. Install by running

npm install --save duck-check

Quick Start

(skip to guide)

Getting started

const { 
 assert, 
 is, 
 check, 
 not, 
 one_of, oneOf,
 either, 
 any 
} = require('duck-check')

Basic checks

check(Number)(1) // -> true
check(Number)("i'm not a number") // -> TypeError

assert(String)('hello world!') // -> true
assert(String)(42) // -> false

is(String)('hello world!')// -> true
is(String)(42)// -> false

is(Date)(new Date()) // -> true
is(Date)('today') // -> false

is(Function)(() => "i'm a function") // -> true

const even = n => n % 2 === 0
is(even)(20) // -> true
is(even)(3) // -> false

Typed Arrays

is([ Number ])([1,2,3]) // -> true
is([ Number ])([1,'2',3]) // -> false
is([ Number ])([]) // -> false
is([ Number ])(1) // -> false

Positional Arrays

is([ Number, String, Boolean ])([1,'a', true]) // -> true
is([ Number, String, Boolean ])([1,false, 'a']) // -> false

Objects

is( { key: String } )( { key: 'value '} ) // -> true
is( { key: String } )( { key: 42 } ) // -> false
is( { key: String } )( { wrong: 'value' } ) // -> false
is( { key: String } )( { key: 'value', other: 42 } ) // -> true

Reusing previous checker functions

const Person = assert({ name: String, age: Number })
assert([ Person ])([ { name: 'John', age: 45 }, { name: 'Jane', age: 55 } ]) // -> true

Mixed Objects and Arrays

is( [ { key: String } ] )( [ { key: 'first' }, { key: 'second' } ] ) // -> true
is( [ { key: String } ] )( [ { key: 'first' }, { wrong: 'second' } ] ) // -> false

Modifiers

not(Number)(null) // -> true
not(Number)(1) // -> false
check(not(Number))(1) // -> TypeError

one_of(Number, String, null)(1) // -> true
one_of(Number, String, null)('a') // -> true
one_of(Number, String, null)(null) // -> true
one_of(Number, String, null)(NaN) // -> false

either([ Number ], { x: Number, y: Number } )( [ 1, 2 ] ) // -> true
either([ Number ], { x: Number, y: Number } )( { x: 1, y: 2 } ) // -> true
either([ Number ], { x: Number, y: Number } )( { x: 1, wrong: 2 } ) // -> false

is({ x: any })({ x: 1 }) // -> true
is({ x: any })({ x: NaN }) // -> true
is({ x: any })({ wrong: 1 }) // -> false
is({ x: either(Number, String)})({x: 1}) // -> true
is({ x: either(Number, String)})({x: false}) // -> false

Guide

Importing:

In Node:

const { check, assert, is, modifiers, not, one_of, oneOf, any, either } = require('duck-check')

ES6 modules:

import { check, assert, is, modifiers, not, one_of, oneOf, any, either } from 'duck-check'

Schema

A schema represents the expected structure or type of your data. It is passed as an argument to the check, assert and other modifier functions.

A valid schema is:

  • A primitive type constructor such as Number, String, Boolean, Function
  • A primitive object, such as null, undefined, NaN
  • Any class constructor
  • An array litteral containing any valid schema (interpreted as a typed array)
  • An array litteral containing multiple valid schemas (interpreted as a positional array)
  • An object litteral with a key and any valid schema as a value
  • A function

Main API

check(schema)(data)

Returns a function that takes data as its argument, and throws a TypeError if the data does not match the schema. Returns undefined otherwise.

is(schema)(data)

Alias for assert

assert(schema)(data)

Returns a function that takes data as its argument, and returns false if the data does not match the schema. Returns true otherwise.

Checking data

Typed Arrays

A typed array is an array where all elements are of one type. For instance, an array of numbers is a typed array.

is([ Number ])( [1,2,3] )
Positional Arrays

A positional array is an array where each position in the array is of a specific type. For instance, an array with a first number, then a string.

is([ Number, String ])( [1, 'a'] )
Objects

An object has keys and values. For instance, an object with a key of key and a value of type String.

is({ key: String })( {key: 'value' })

The test passes if all keys declared in the schema object are defined in the data, and if the value of each key matches the type declared in the schema. Keys declared in the data but not in the schema are ignored.

To check for a key with any value, use the any modifier.

Mixed Objects and Arrays

Since any schema can contain other schemas, you can check for arrays of objects, objects containing arrays, etc... You can compose your schemas as needed without limit (as long as they are not recursive).

Functions

If you pass a function in the schema, it will be called with the data as its argument. If the function returns true, the test passes. if it returns false, or throws an error, the test fails.

This means previous calls to check or assert can be used in any schema.

const Person = assert({ name: String, age: Number }) // ! \\ Do not use this naming convention in project involving OOP classes!
assert([ Person ])([ { name: 'John', age: 45 }, { name: 'Jane', age: 55 } ]) // -> true

You can also define your own functions as needed.

const even = n => n % 2 === 0
is([even])([20, 22]) // -> true
is([even])([20, 21]) // -> false
Modifiers

Modifiers take a schema, and alter the result of the check.

A modifier can be used anywhere in a schema, or even with other modifiers. For instance, you can declare an array of neither numbers nor strings.

is([ not(either(Number, String)) ])([1, 'a']) // -> false

any(data)

A function that always returns true. Do not call the function when declaring the schema.

is(any)() // -> true

not(schema)

Returns a function that takes in data and returns the negation of check(schema)(data).

not(Number)(null) // -> true
not(Number)(1) // -> false
check(not(Number))(1) // -> TypeError

either(schema_a, schema_b)

Returns a function that takes in data and returns true if either schemas match the data.

either([ Number ], { x: Number, y: Number } )( [ 1, 2 ] ) // -> true
either([ Number ], { x: Number, y: Number } )( { x: 1, y: 2 } ) // -> true
either([ Number ], { x: Number, y: Number } )( { x: 1, wrong: 2 } ) // -> false

oneOf(...args)

alias of one_of

one_of(...args)

Returns a function that takes in data and returns true if one of the schemas passed as arguments match the data.

one_of(Number, String, null)(1) // -> true
one_of(Number, String, null)('a') // -> true
one_of(Number, String, null)(null) // -> true
one_of(Number, String, null)(NaN) // -> false

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