JavaScript浅拷贝和深拷贝

JavaScript浅拷贝和深拷贝

浅拷贝

let obj = {
    a: 1,
    cat: {
        name: 1,
        age: 2,
        tags: ["小叮当"],
    },
};
let copy = { ...obj };
copy.cat.name = 2;
console.log(copy.cat.name, obj.cat.name);
// 2 2

let obj = {
    a: 1,
    cat: {
        name: 1,
        age: 2,
        tags: ["小叮当"],
    },
};
let copy = { ...obj };
copy.cat = { a: 1 };
console.log(copy.cat, obj.cat);
// { a: 1 } { name: 1, age: 2, tags: [ '小叮当' ] }

深拷贝

let obj = {
    a: 1,
    cat: {
        name: 1,
        age: 2,
        tags: ["小叮当"],
    },
};
let copy = JSON.parse(JSON.stringify(obj));
copy.cat.age = 10;
console.log(copy.cat.age, obj.cat.age);
// 10 2

• 会抛弃对象的constructor，所有对象的constructor都会变为Object

• 无法实现对函数、RegExp等特殊对象的克隆

• 循环引用会报错

let obj = {
    a: 1,
    age: obj.a,
    cat: {
        name: 1,
        age: 2,
    },
};
let copy = JSON.parse(JSON.stringify(obj));
copy.cat.age = 10;
console.log(copy.cat.age, obj.cat.age);
// ReferenceError: Cannot access 'obj' before initialization

let obj = {
  a: 1,
  b: /1/g,
  cat: {
    name: 1,
    age: 2,
    callMe: function () {
      console.log("me");
    },
  },
  set: new Set([1, 2, 3]),
  map: new Map([
    [1, 2],
    [3, 4],
  ]),
};

// 深拷贝函数
function deepCopy(target) {
  const wm = new WeakMap();

  // 判断类型
  function getType(target) {
    return Object.prototype.toString.call(target).slice(8, -1);
  }
  // 递归处理
  function handleDeepCopy(target) {
    if (getType(target) === "Array") {
      let arr = [];
      for (let i in target) {
        arr.push(handleDeepCopy(target[i]));
      }
      return arr;
    } else if (getType(target) === "Object") {
      let obj = Object.create(Object.getPrototypeOf(target));
      if (wm.has(target)) {
        // 解决循环引用，避免重复递归
        return wm.get(target);
      }

      wm.set(target, obj);
      for (let i of Object.keys(target)) {
        obj[i] = handleDeepCopy(target[i]);
      }
      
      return obj;
    } else if (getType(target) === "Function") {
      const fn = target.toString();
      return new Function("return " + fn)();
    } else if (getType(target) === "RegExp" || getType(target) === "Date") {
      return new target.constructor(target);
    } else if (getType(target) === "Set") {
      const set = new Set();
      target.forEach((val) => {
        set.add(handleDeepCopy(val));
      });
      return set;
    } else if (getType(target) === "Map") {
      const map = new Map();
      for (let item of target) {
        map.set(handleDeepCopy(item[0]), handleDeepCopy(item[1]));
      }
      return map;
    } else if (!(target instanceof Object)) {
      // 原始类型
      return target;
    } else {
      console.error("未拦截的类型 ", target);
    }
  }

  return handleDeepCopy(target);
}

// 封装成一个处理函数
// function deepCopy(target) {
//     if (getType(target) !== "Array" && getType(target) !== "Object") {
//         throw new Error("必须传入一个对象或者数组");
//     }

//     let copy = Object.create(target.prototype || null);
//     for (let i in target) {
//         copy[i] = deepCopy(target[i]);
//     }
//     return copy;
// }

// 验证是否拷贝成功
const copyObj = deepCopy(obj);
console.log(copyObj);
/*
[Object: null prototype] {
  a: 1,
  b: /1/g,
  cat: { name: 1, age: 2, callMe: [Function (anonymous)] },
  set: Set(3) { 1, 2, 3 },
  map: Map(2) { 1 => 2, 3 => 4 }
}
*/
// 验证深拷贝
copyObj.cat.name = "阿花";
console.log(copyObj, obj);
/*
{
  a: 1,
  b: /1/g,
  cat: { name: '阿花', age: 2, callMe: [Function (anonymous)] },
  set: Set(3) { 1, 2, 3 },
  map: Map(2) { 1 => 2, 3 => 4 }
}
{
  a: 1,
  b: /1/g,
  cat: { name: 1, age: 2, callMe: [Function: callMe] },
  set: Set(3) { 1, 2, 3 },
  map: Map(2) { 1 => 2, 3 => 4 }
}
*/
// 验证函数拷贝是否成功
copyObj.cat.callMe();
// me

// 验证循环引用
const o = { a: {} };
o.a.o = o;
console.log(deepCopy(o));