merge function for mingo

merge-objects.js

function isArray(v) { return !!v && v.constructor === Array }
function isObject(v) { return !!v && v.constructor === Object }
function merge(target, obj, opt) {
  // take care of null inputs
  if (!isObject(target) && !isArray(obj) || !isObject(target) && !isArray(obj)) return obj
  if (!(isArray(target) && isArray(obj) || isObject(target) && isObject(obj))) {
    throw Error('mismatched types. must both be array or object')
  }

  opt = opt || {}
  opt.flatten = opt.flatten || false

  if (isArray(target)) {
    Array.prototype.push.apply(target, obj)
    let flatten = opt.flatten && !target.some((v) => !isObject(v))
    if (flatten) {
      let tgt = target[0]
      for (let i = 1; i < target.length; i++) {
        tgt = merge(tgt, target[i])
      }
      target.splice(0, target.length)
      target.push(tgt)
    }
  } else {
    Object.keys(obj).forEach((k,v) => {
      if (target.hasOwnProperty(k)) {
        target[k] = merge(target[k], obj[k])
      } else {
        target[k] = obj[k]
      }
    })
  }

  return target
}