Either Functional Error Handling Strategy

Either.js

const Right = x =>
({
  map: f => Right(f(x)),
  fold: (f,g) => g(x),
  inspect: f => f(`Right(${x})`)
})


const Left = x =>
({
  map: f => Left(x),
  fold:(f,g) => f(x),
  inspect: f => f(`Left(${x})`)
})

//This is where the actual error handling logic resides.
const fromNullable = (data) =>  data != null ? Right(data): Left(null)

//there shoudl only ever be one expression in a pure function, so return obj or null 
const findColor = (name) => fromNullable({black:'#000', white:'#fff'}[name])


//Failure Case - Notice that both functions have a failure case, but truthy executes right, falsey left.
let greyExists = findColor('grey').fold(e=>"error", data=>data)
console.log(greyExists)

//Successful Case
let blackExists= findColor('black').fold(e=>"error", data=>data)
console.log(blackExists)