moy-fp/src/Functor/Identity/index.js

A functional programming library.

/**
 * Identity is a Functor, Monad and Applicative
 * can map
 * can join
 * can chain
 * can ap
 * always use for containing a value in a box
 * you may not need it if you are not sensitive in functional programming
 */
const Identity = value => Object.seal(
  Object.create(null, {
    value: {
      value,
    },
    [Symbol.toStringTag]: {
      value: 'Identity',
    },
    map: {
      value: function map(fn){
        return Identity.of(fn(this.value))
      },
    },
    join: {
      value: function join(){
        return this.value
      },
    },
    chain: {
      value: function chain(fn){
        return fn(this.value)
      },
    },
    ap: {
      value: function ap(I){
        return I.map(this.value)
      },
    },
  })
)

/**
 * Functor Identity => a -> Identity a
 */
Identity.of = Identity

export default Identity