typeforce

Another biased type checking solution for Javascript.

Exception messages may change between patch versions, as often the patch will change some behaviour that was unexpected and naturally it results in a different error message.

Examples

const typeforce = require('typeforce')

// supported primitives 'Array', 'Boolean', 'Buffer', 'Number', 'Object', 'String'
typeforce('Array', [])

typeforce('Number', [])
// TypeError: Expected Number, got Array

// array types
typeforce(['Object'], [{}])
typeforce(typeforce.arrayOf('Object'), [{}, {}, {}])

// enforces object properties 
typeforce({
  foo: 'Number'
}, {
  foo: 'bar'
})
// TypeError: Expected property "foo" of type Number, got String "bar"

// maybe types
typeforce('?Number', 2)
typeforce('?Number', null)
typeforce(typeforce.maybe(typeforce.Number), 2)
typeforce(typeforce.maybe(typeforce.Number), null)

// sum types
typeforce(typeforce.anyOf('String', 'Number'), 2)
typeforce(typeforce.allOf({ x: typeforce.Number }, { y: typeforce.Number }), {
  x: 1,
  y: 2
})

// value types
typeforce(typeforce.value(3.14), 3.14)

// custom types
function LongString (value, strict) {
  if (!typeforce.String(value)) return false
  if (value.length !== 32) return false
  return true
}

typeforce(LongString, '00000000000000000000000000000000')
// => OK!

typeforce(LongString, 'not long enough')
// TypeError: Expected LongString, got String 'not long enough'

Protips:

// use precompiled primitives for high performance
typeforce(typeforce.Array, array)

// or just precompile a template
const type = {
  foo: 'Number',
  bar: '?String'
}

const fastType = typeforce.compile(type)
// fastType => typeforce.object({
//   foo: typeforce.Number,
//   bar: typeforce.maybe(typeforce.String)
// })

// use strictness for recursive types to enforce whitelisting properties
typeforce({
  x: 'Number'
}, { x: 1 }, true)
// OK!

typeforce({
  x: 'Number'
}, { x: 1, y: 2 }, true)
// TypeError: Unexpected property 'y' of type Number

Protips (extended types):

typeforce(typeforce.tuple('String', 'Number'), ['foo', 1])
// OK!

typeforce(typeforce.tuple('Number', 'Number'), ['not a number', 1])
// TypeError: Expected property "0" of type Number, got String 'not a number'

typeforce(typeforce.map('Number'), {
  'anyKeyIsOK': 1
})
// OK!

typeforce(typeforce.map('Number', typeforce.HexN(8)), {
  'deadbeef': 1,
  'ffff0000': 2
})
// OK!

function Foo () {
  this.x = 2
}

typeforce(typeforce.quacksLike('Foo'), new Foo())
// OK!

// Note, any Foo will do
typeforce(typeforce.quacksLike('Foo'), new (function Foo() {}))
// OK!

Protips (no throw)

const typeforce = require('typeforce/nothrow')
const value = 'foobar'

if (typeforce(typeforce.Number, value)) {
  // didn't throw!
  console.log(`${value} is a number`) // never happens
} else {
  console.log(`Oops, ${typeforce.error.message}`)
  // prints 'Oops, Expected Number, got String foobar'
}

Protips (async)

const typeforce = require('typeforce/async')

typeforce(typeforce.Number, value, function (err) {
  if (err) return console.log(`Oops, ${typeforce.error.message}`)

  console.log(`${value} is a number`) // never happens
})

WARNING: Be very wary of using the quacksLike type, as it relies on the Foo.name property. If that property is mangled by a transpiler, such as uglifyjs, you will have a bad time.