javascript深拷貝是初學(xué)者甚至有經(jīng)驗(yàn)的開發(fā)著,都會(huì)經(jīng)常遇到問(wèn)題,下面這篇文章主要給大家介紹了關(guān)于JavaScript深拷貝的幾種實(shí)現(xiàn)方法,文中通過(guò)實(shí)例代碼介紹的非常詳細(xì),需要的朋友可以參考下

淺拷貝與深拷貝

淺拷貝是創(chuàng)建一個(gè)新對(duì)象，這個(gè)對(duì)象有著原始對(duì)象屬性值的拷貝。如果屬性是基本類型，拷貝的就是基本類型的值，如果屬性是引用類型，拷貝的是內(nèi)存地址。如果不進(jìn)行深拷貝，其中一個(gè)對(duì)象改變了對(duì)象的值，就會(huì)影響到另一個(gè)對(duì)象的值。

深拷貝是將一個(gè)對(duì)象從內(nèi)存中完整的拷貝一份出來(lái),從堆內(nèi)存中開辟一個(gè)新的區(qū)域存放新對(duì)象,且修改新對(duì)象不會(huì)影響原對(duì)象。

1.JSON.parse(JSON.stringify(obj))

一般情況下對(duì)普通對(duì)象需要進(jìn)行深拷貝，可以使用這種方法進(jìn)行深拷貝操作，這種是最簡(jiǎn)單且代碼量最少的深拷貝方法。

let a = {a:1,b:2}
let b = JSON.parse(JSON.stringify(a))
a.a = 11
console.log(a)//{a:1,b:2}
console.log(b)//{a:11,b:2}

1.1 JSON.parse(JSON.stringify(obj))深淺拷貝的缺陷

let a = {
    name: 'Jack',
    age: 18,
    hobbit: ['sing', {type: 'sports', value: 'run'}],
    score: {
        math: 'A',
    },
    run: function() {},
    walk: undefined,
    fly: NaN,
    cy: null,
    date: new Date()
}
let b = JSON.parse(JSON.stringify(a))
console.log(b)
// {
//     age: 18,
//     cy: null,
//     date: "2022-05-15T08:04:06.808Z"
//     fly: null,
//     hobbit: (3) ["dance", "sing", {…}],
//     name: "Jack",
//     score: {math: "A"},
// }

取不到值為 undefined 的 key；如果對(duì)象里有函數(shù)，函數(shù)無(wú)法被拷貝下來(lái)；無(wú)法拷貝copyObj對(duì)象原型鏈上的屬性和方法；對(duì)象轉(zhuǎn)變?yōu)?date 字符串。

2.普通遞歸函數(shù)實(shí)現(xiàn)深拷貝

function deepClone(source) {
  if (typeof source !== 'object' || source == null) {
    return source;
  }
  const target = Array.isArray(source) ? [] : {};
  for (const key in source) {
    if (Object.prototype.hasOwnProperty.call(source, key)) {
      if (typeof source[key] === 'object' && source[key] !== null) {
        target[key] = deepClone(source[key]);
      } else {
        target[key] = source[key];
      }
    }
  }
  return target;
}

2.1解決循環(huán)引用和symblo類型

function cloneDeep(source, hash = new WeakMap()) {
  if (typeof source !== 'object' || source === null) {
    return source;
  }
  if (hash.has(source)) {
    return hash.get(source);
  }
  const target = Array.isArray(source) ? [] : {};
  Reflect.ownKeys(source).forEach(key => {
    const val = source[key];
    if (typeof val === 'object' && val != null) {
      target[key] = cloneDeep(val, hash);
    } else {
      target[key] = val;
    }
  })
  return target;
}

3.兼容多種數(shù)據(jù)類型

const deepClone = (source, cache) => {
  if(!cache){
    cache = new Map() 
  }
  if(source instanceof Object) { // 不考慮跨 iframe
    if(cache.get(source)) { return cache.get(source) }
    let result 
    if(source instanceof Function) {
      if(source.prototype) { // 有 prototype 就是普通函數(shù)
        result = function(){ return source.apply(this, arguments) }
      } else {
        result = (...args) => { return source.call(undefined, ...args) }
      }
    } else if(source instanceof Array) {
      result = []
    } else if(source instanceof Date) {
      result = new Date(source - 0)
    } else if(source instanceof RegExp) {
      result = new RegExp(source.source, source.flags)
    } else {
      result = {}
    }
    cache.set(source, result)
    for(let key in source) { 
      if(source.hasOwnProperty(key)){
        result[key] = deepClone(source[key], cache) 
      }
    }
    return result
  } else {
    return source
  }
}

4.jQuery.extend()方法

可以使用$.extend進(jìn)行深拷貝
$.extend(deepCopy, target, object1, [objectN])//第一個(gè)參數(shù)為true,就是深拷貝

let a = {
    a: 1,
    b: { d:8},
    c: [1, 2, 3]
};
let b = $.extend(true, {}, a);
console.log(a.b.d === b.b.d); // false

4.1 jQuery.extend 源碼

jQuery.extend = jQuery.fn.extend = function() {
  var options,
    name,
    src,
    copy,
    copyIsArray,
    clone,
    target = arguments[0] || {},
    i = 1,
    length = arguments.length,
    deep = false;

  // Handle a deep copy situation
  if (typeof target === "boolean") {
    deep = target;

    // Skip the boolean and the target
    target = arguments[i] || {};
    i++;
  }

  // Handle case when target is a string or something (possible in deep copy)
  if (typeof target !== "object" && !jQuery.isFunction(target)) {
    target = {};
  }