try-catch.js

const safeChain = (state, mapper) => {
  try {
    return mapper(state)
  } catch (e) {
    return undefined
  }
}

module.exports = {safeChain}

safe-chain

core

const symbol = Symbol('safe')

const isNullish = value => value === undefined || value === null
const isPack = pack => typeof pack === 'object' && symbol in pack

const pack = value => ({ [symbol]: value })
const unpack = pack => pack[symbol]

const toProxy = (state, revokes) => {
  const wrap = pack(state)
  const handler = trap(revokes)
  const {proxy, revoke} = Proxy.revocable(wrap, handler)
  revokes.push(revoke)
  return proxy
}

const trap = (revokes) => {
  return {
    get (target, key) {
      const unpacked = unpack(target)
      return key === symbol ?
        unpacked :
        toProxy(isNullish(unpacked) ? undefined : unpacked[key], revokes)
    }
  }
}

module.exports = {toProxy, isPack, unpack}

index

const {toProxy, isPack, unpack} = require('./core')

const safeChain = (state, mapper) => {
  const revokes = []
  const proxy = toProxy(state, revokes)
  const mappedResult = mapper(proxy)
  const result = isPack(mappedResult) ? unpack(mappedResult) : mappedResult

  revokes.forEach(fn => fn())
  return result
}

module.exports = {safeChain}

example

const {safeChain} = require('./index')

const backendApi = {
  fetchResponse() {
    this.response = {
      result: { message: 'Success' },
      status: 200,
      statusCode: 'Ok'
    }
  },
  response: null,
  get result () {
    return safeChain(this.response, ({result}) => result)
  }
}

console.log(backendApi.result) // undefined
backendApi.fetchResponse()
console.log(backendApi.result) // { message: 'Success' }