deepCopy.js

function deepCopy (target) {
  if (
    target === null
    || typeof target === 'number'
    || typeof target === 'boolean'
    || typeof target === 'string'
    || typeof target === undefined
  ) return target

  if (Array.isArray(target)) {
    return target.map(item => deepCopy(item))
  } 

  if (target instanceof Date) {
    return new Date(target)
  }

  if (typeof target === 'object') {
    const _obj = {}
    for (const key in target) {
      _obj[key] = deepCopy(target[key])
    }
    return _obj
  }

  return undefined
}

deepGet.js

function deepGet (obj, path) {
  const arr = path.split('.')

  for (const item of arr) {
    if (obj[item] === undefined) return undefined

    obj = obj[item]
  }

  return obj
}

deepSet.js

function deepSet(obj, path, value) {
  const arr = path.split('.')

  for (let i = 0; i < arr.length; i++) {
    if (i === arr.length - 1) { 
      obj[arr[i]] = value
    } else if (obj[arr[i]] === undefined) {
      obj = obj[arr[i]] = {}
    } else {
      obj = obj[arr[i]]
    }
  }
}