实现assign-deep

[AlexZ33]

• Recursive Object.assign() Deeply assign the enumerable properties of source objects to a destination object.

https://github.com/jonschlinkert/assign-deep

/*!
 * assign-deep <https://github.com/jonschlinkert/assign-deep>
 *
 * Copyright (c) 2017-present, Jon Schlinkert.
 * Released under the MIT License.
 */

'use strict';

const toString = Object.prototype.toString;
const assignSymbols = require('assign-symbols');

const isValidKey = key => {
  return key !== '__proto__' && key !== 'constructor' && key !== 'prototype';
};

const assign = module.exports = (target, ...args) => {
  let i = 0;
  if (isPrimitive(target)) target = args[i++];
  if (!target) target = {};
  for (; i < args.length; i++) {
    if (isObject(args[i])) {
      for (const key of Object.keys(args[i])) {
        if (isValidKey(key)) {
          if (isObject(target[key]) && isObject(args[i][key])) {
            assign(target[key], args[i][key]);
          } else {
            target[key] = args[i][key];
          }
        }
      }
      assignSymbols(target, args[i]);
    }
  }
  return target;
};

function isObject(val) {
  return typeof val === 'function' || toString.call(val) === '[object Object]';
}

function isPrimitive(val) {
  return typeof val === 'object' ? val === null : typeof val !== 'function';
}