手写深拷贝

方法一：用JSON

const b = JSON.parse(JSON.stringify(a))

缺点：

• 不支持 Date、正则、undefined、函数等数据
• 不支持引用（即环状结构）

方法二： 使用递归

const deepClone = (a, cache) => {
  if (!cache) { 
    cache = new Map() // 缓存不能全局，最好临时创建并递归传递
  } 
  if (a instanceof Object) { // 不考虑跨 iframe
    if (cache.get(a)) { return cache.get(a) }
    let result
    if (a instanceof Function) {
      if (a.prototype) {  // 有 prototype 就是普通函数
        result = function () { return a.apply(this, arguments) }
      } else {
        result = (...args) => { return a.call(undefined, ...args) }
      }
    } else if (a instanceof Array) {
      result = []
    } else if (a instanceof Date) {
      result = new Date(a - 0)
    } else if (a instanceof RegExp) {
      result = new RegExp(a.source, a.flags)
    } else {
      result = {}
    }
    cache.set(a, result)
    for (let key in a) {
      if (a.hasOwnProperty(key)) {
        result[key] = deepClone(a[key], cache)
      }
    }
    return result
  } else {
    return a
  }
}

调用

const a = {
  number: 1,
  bool: false,
  str: 'hi',
  empty1: undefined,
  empty2: null,
  array: [{name: 'Bumble', age: 18}, {name: 'Tom', age: 19}],
  date: new Date(2022, 10, 20, 12, 30, 0),
  regex: /.(j|t)sx/i,
  obj: {name: 'Bumble', age: 18},
  f1: (a, b) => a + b,
  f2: function (a, b) {
    return a + b
  }
}
a.self = a
const b = deepClone(a)
b.self === b // true
b.self = 'hi'
a.self !== 'hi' //true