js 深拷贝

转自：https://github.com/shfshanyue/Daily-Question/issues/203#issuecomment-888238489

/**
 * 深拷贝关注点:
 * 1. JavaScript内置对象的复制: Set、Map、Date、Regex等
 * 2. 循环引用问题
 * @param {*} object 
 * @returns 
 */
function deepClone(source, memory) {
  const isPrimitive = (value) => {
    return /Number|Boolean|String|Null|Undefined|Symbol|Function/.test(Object.prototype.toString.call(value));
  }
  let result = null;

  memory || (memory = new WeakMap());
  // 原始数据类型及函数
  if (isPrimitive(source)) {
    console.log('current copy is primitive', source);
    result = source;
  }
  // 数组
  else if (Array.isArray(source)) {
    result = source.map(value => deepClone(value, memory));
  }
  // 内置对象Date、Regex
  else if (Object.prototype.toString.call(source) === '[object Date]') {
    result = new Date(source);
  }
  else if (Object.prototype.toString.call(source) === '[object Regex]') {
    result = new RegExp(source);
  }
  // 内置对象Set、Map
  else if (Object.prototype.toString.call(source) === '[object Set]') {
    result = new Set();
    for (const value of source) {
      result.add(deepClone(value, memory));
    }
  }
  else if (Object.prototype.toString.call(source) === '[object Map]') {
    result = new Map();
    for (const [key, value] of source.entries()) {
      result.set(key, deepClone(value, memory));
    }
  }
  // 引用类型
  else {
    if (memory.has(source)) {
      result = memory.get(source);
    } else {
      result = Object.create(null);
      memory.set(source, result);
      Object.keys(source).forEach(key => {
        const value = source[key];
        result[key] = deepClone(value, memory);
      });
    }
  }
  return result;
}