deep-merge-map.js

/* eslint-disable no-use-before-define */

const isArr = Array.isArray
const isMap = (value) => value instanceof Map
const isObj = (value) => typeof value === "object"

const canMerge = (value) =>
  Boolean (value) &&
  isObj (value) &&
  !(/^\[object (?:Date|RegExp)\]$/)
    .test (Object.prototype.toString.call (value))

const emptyObj = (value) => (Array.isArray (value) ? [] : new Map ())

const cloneObj = (value) =>
  (canMerge (value) ? merge (emptyObj (value), value) : value)

const mergeArr = (target, source) =>
  (isArr (target) && isArr (source) ? target.concat (source) : source)
    .map (cloneObj)

const mergeMap = (target, source) => {
  for (const key of source.keys ()) {
    target.set (
      key,
      merge (target.has (key) && target.get (key), source.get (key))
    )
  }

  return target
}

const objToMap = (value) => new Map (Object.entries (value))

// const mapToObj = (value) =>
//   Array.from (value).reduce ((target, [k, v]) => {
//     target[k] = v

//     return target
//   }, {})

const merge = (... sources) =>
  sources.reduce ((target, source) => {
    if (isArr (source)) {
      return mergeArr (target, source)
    } else if (canMerge (source)) {
      return mergeMap (
        isMap (target) ? target : objToMap (target),
        isMap (source) ? source : objToMap (source)
      )
    }

    return cloneObj (source)
  }, new Map ())

module.exports = merge