深拷贝

function deepClone(obj) {
  if (obj === null || typeof obj !== "object") {
    return obj;
  }

  if (obj instanceof Date) {
    return new Date(obj);
  }

  if (obj instanceof Array) {
    const cloneArray = [];
    for (let i = 0; i < obj.length; i++) {
      cloneArray[i] = deepClone(obj[i]);
    }
    return cloneArray;
  }

  if (obj instanceof Object) {
    const cloneObj = {};
    for (let key in obj) {
      if (obj.hasOwnProperty(key)) {
        cloneObj[key] = deepClone(obj[key]);
      }
    }
    return cloneObj;
  }
}

在实际开发中通常不会这么使用深拷贝，ES6 中的 JSON.parse(JSON.stringify(obj))也可以用于深拷贝，但有一定的限制比如不能用于复制函数和循环引用

function deepClone2(obj) {
  const cloneObj = JSON.parse(JSON.stringify(obj));
  return cloneObj;
}

验证

const originalObject = {
  name: "John",
  age: 30,
  address: {
    city: "New York",
    country: "USA",
  },
  hobbies: ["reading", "traveling"],
};

const copiedObject = deepClone(originalObject);
console.log(copiedObject);

浅拷贝

function shallowClone(obj) {
  if (obj === null || typeof obj !== "object") {
    return obj;
  }

  if (obj instanceof Array) {
    const cloneArray = [];
    for (let i = 0; i < obj.length; i++) {
      cloneArray[i] = obj[i];
    }
    return cloneArray;
  }

  if (obj instanceof Object) {
    const cloneObject = {};
    for (let key in obj) {
      if (obj.hasOwnProperty(key)) {
        cloneObject[key] = obj[key];
      }
    }
    return cloneObject;
  }
}

浅拷贝与深拷贝的区别在于，深拷贝是层级式的将原数据完全拷贝成为一份新的数据，浅拷贝仅仅是对数据的第一层进行拷贝。当改变拷贝数据的深层数据时，浅拷贝会影响原数据而深拷贝不会影响原数据。
验证

const originalObject = {
  name: "John",
  age: 30,
  hobbies: ["reading", "traveling"],
};

const copiedObject = shallowClone(originalObject);
console.log(copiedObject);

copiedObject.name = "Alice";
copiedObject.hobbies.push("swimming");

console.log(originalObject);