@iin-mdc/koa-utils/lib/deep-merge-with-symbols.js

"use strict"

// FROM lodash
function isObject(value) {
  // We do not want to deep merge a function
  //return type == "function" || (!!value && type == "object")
  return (!!value && typeof(value) === "object")
}

function deepMerge(...args) {
  let target = args[0],
      len    = args.length,
      i      = 0

  while (++i < len) {
    let provider   = args[i],
        allKeys    = Object.getOwnPropertySymbols(provider).concat(Object.keys(provider)),
        allKeysLen = allKeys.length,
        j          = -1

    while (++j < allKeysLen) {
      let key         = allKeys[j],
          targetVal   = target[key],
          providerVal = provider[key]

      if (Object.prototype.hasOwnProperty.call(target, key) && isObject(targetVal) && isObject(providerVal)) {
        deepMerge(targetVal, providerVal)
      } else {
        target[key] = providerVal
      }
    }
  }

  return target
}

module.exports = deepMerge