1.0.0 • Published 7 years ago

to-factory v1.0.0

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7 years ago


Convert classes into factory functions.

Allows ES6 classes to be instantiated with or without new.

Allows your API consumers to not need to divine (there's no built-in way to know) which functions you intend to be called with new, and which functions are to be called without.


without to-factory

Must call a class with new, cannot call class as a function:

class Person {
  constructor(name) {
    this.name = name

new Person('alice') // ok
Person('bob') // TypeError: Cannot call a class as a function

with to-factory

Call a class with new or as a function:

// exact same Person class as above example

Person = toFactory(Person)

const personA = new Person('created with new')
console.log(personA.name) // => 'created with new'

const personB = Person('created without new')
console.log(personB.name) // => 'created without new'

Inheritance, etc all works as expected

// Inheritance works as expected
class BigPerson extends Person {
  constructor(name) {

BigPerson = toFactory(BigPerson)

const bigPersonA = new BigPerson('created with new')
console.log(bigPersonA.name) // => 'CREATED WITH NEW'

const bigPersonB = BigPerson('created without new')
console.log(bigPersonB.name) // => 'CREATED WITHOUT NEW'


The "can't call without new" restriction on ES6 classes create a needless incompatibility between tools which accept classes and tools which accept regular functions – there is no built-in means for a tol to determine whether a function wants be called with new or without new, it just has to pick one and hope for the best.

While it's true that some real-world functions insist on being constructors in much the same way, at least it is possible to patch the library and/or submit a pull request explaining that requiring new is uneccessarily rigid and provides little benefit when it's entirely possible to transparently handle both cases. With ES6 classes we have no option to just patch the library as this rigidity is baked right into the implementation.

See Also