我有一个对象x。我想将其复制为对象y,这样对y的更改不会修改x。我意识到复制从内置JavaScript对象派生的对象会导致额外的、不需要的财产。这不是问题,因为我正在复制我自己的一个文字构造对象。
如何正确克隆JavaScript对象?
我有一个对象x。我想将其复制为对象y,这样对y的更改不会修改x。我意识到复制从内置JavaScript对象派生的对象会导致额外的、不需要的财产。这不是问题,因为我正在复制我自己的一个文字构造对象。
如何正确克隆JavaScript对象?
当前回答
老问题的新答案!如果您有幸将ECMAScript 2016(ES6)与Spread Syntax一起使用,这很简单。
keepMeTheSame = {first: "Me!", second: "You!"};
cloned = {...keepMeTheSame}
这为对象的浅层副本提供了一种干净的方法。创建一个深度副本,意味着为每个递归嵌套对象中的每个值创建一个新副本,这需要使用上面更重的解决方案。
JavaScript不断发展。
其他回答
根据Apple JavaScript编码指南:
// Create an inner object with a variable x whose default
// value is 3.
function innerObj()
{
this.x = 3;
}
innerObj.prototype.clone = function() {
var temp = new innerObj();
for (myvar in this) {
// this object does not contain any objects, so
// use the lightweight copy code.
temp[myvar] = this[myvar];
}
return temp;
}
// Create an outer object with a variable y whose default
// value is 77.
function outerObj()
{
// The outer object contains an inner object. Allocate it here.
this.inner = new innerObj();
this.y = 77;
}
outerObj.prototype.clone = function() {
var temp = new outerObj();
for (myvar in this) {
if (this[myvar].clone) {
// This variable contains an object with a
// clone operator. Call it to create a copy.
temp[myvar] = this[myvar].clone();
} else {
// This variable contains a scalar value,
// a string value, or an object with no
// clone function. Assign it directly.
temp[myvar] = this[myvar];
}
}
return temp;
}
// Allocate an outer object and assign non-default values to variables in
// both the outer and inner objects.
outer = new outerObj;
outer.inner.x = 4;
outer.y = 16;
// Clone the outer object (which, in turn, clones the inner object).
newouter = outer.clone();
// Verify that both values were copied.
alert('inner x is '+newouter.inner.x); // prints 4
alert('y is '+newouter.y); // prints 16
史蒂夫
(以下内容主要是@Maciej Bukowski、@A.Levy、@Jan Turoğ、@Redu的回答,以及@LeviRoberts、@RobG的评论的整合,非常感谢他们!!!)
深度复制?-对!(大部分);浅拷贝?-不!(代理除外)。
我真诚欢迎大家来测试clone()。此外,defineProp()设计用于轻松快速地(重新)定义或复制任何类型的描述符。
作用
function clone(object) {
/*
Deep copy objects by value rather than by reference,
exception: `Proxy`
*/
const seen = new WeakMap()
return clone(object)
function clone(object) {
if (object !== Object(object)) return object /*
—— Check if the object belongs to a primitive data type */
if (object instanceof Node) return object.cloneNode(true) /*
—— Clone DOM trees */
let _object // The clone of object
switch (object.constructor) {
case Array:
case Object:
_object = cloneObject(object)
break
case Date:
_object = new Date(+object)
break
case Function:
_object = copyFn(object)
break
case RegExp:
_object = new RegExp(object)
break
default:
switch (Object.prototype.toString.call(object.constructor)) {
// // Stem from:
case "[object Function]":
switch (object[Symbol.toStringTag]) {
case undefined:
_object = cloneObject(object) // `class`
break
case "AsyncFunction":
case "GeneratorFunction":
case "AsyncGeneratorFunction":
_object = copyFn(object)
break
default:
_object = object
}
break
case "[object Undefined]": // `Object.create(null)`
_object = cloneObject(object)
break
default:
_object = object // `Proxy`
}
}
return _object
}
function cloneObject(object) {
if (seen.has(object)) return seen.get(object) /*
—— Handle recursive references (circular structures) */
const _object = Array.isArray(object)
? []
: Object.create(Object.getPrototypeOf(object)) /*
—— Assign [[Prototype]] for inheritance */
seen.set(object, _object) /*
—— Make `_object` the associative mirror of `object` */
Reflect.ownKeys(object).forEach(key =>
defineProp(_object, key, { value: clone(object[key]) }, object)
)
return _object
}
}
function copyPropDescs(target, source) {
Object.defineProperties(target,
Object.getOwnPropertyDescriptors(source)
)
}
function convertFnToStr(fn) {
let fnStr = String(fn)
if (fn.name.startsWith("[")) // isSymbolKey
fnStr = fnStr.replace(/\[Symbol\..+?\]/, '')
fnStr = /^(?!(async )?(function\b|[^{]+?=>))[^(]+?\(/.test(fnStr)
? fnStr.replace(/^(async )?(\*)?/, "$1function$2 ") : fnStr
return fnStr
}
function copyFn(fn) {
const newFn = new Function(`return ${convertFnToStr(fn)}`)()
copyPropDescs(newFn, fn)
return newFn
}
function defineProp(object, key, descriptor = {}, copyFrom = {}) {
const { configurable: _configurable, writable: _writable }
= Object.getOwnPropertyDescriptor(object, key)
|| { configurable: true, writable: true }
const test = _configurable // Can redefine property
&& (_writable === undefined || _writable) // Can assign to property
if (!test || arguments.length <= 2) return test
const basisDesc = Object.getOwnPropertyDescriptor(copyFrom, key)
|| { configurable: true, writable: true } // Custom…
|| {}; // …or left to native default settings
["get", "set", "value", "writable", "enumerable", "configurable"]
.forEach(attr =>
descriptor[attr] === undefined &&
(descriptor[attr] = basisDesc[attr])
)
const { get, set, value, writable, enumerable, configurable }
= descriptor
return Object.defineProperty(object, key, {
enumerable, configurable, ...get || set
? { get, set } // Accessor descriptor
: { value, writable } // Data descriptor
})
}
//测试
const obj0 = {
u: undefined,
nul: null,
t: true,
num: 9,
str: "",
sym: Symbol("symbol"),
[Symbol("e")]: Math.E,
arr: [[0], [1, 2]],
d: new Date(),
re: /f/g,
get g() { return 0 },
o: {
n: 0,
o: { f: function (...args) { } }
},
f: {
getAccessorStr(object) {
return []
.concat(...
Object.values(Object.getOwnPropertyDescriptors(object))
.filter(desc => desc.writable === undefined)
.map(desc => Object.values(desc))
)
.filter(prop => typeof prop === "function")
.map(String)
},
f0: function f0() { },
f1: function () { },
f2: a => a / (a + 1),
f3: () => 0,
f4(params) { return param => param + params },
f5: (a, b) => ({ c = 0 } = {}) => a + b + c
}
}
defineProp(obj0, "s", { set(v) { this._s = v } })
defineProp(obj0.arr, "tint", { value: { is: "non-enumerable" } })
obj0.arr[0].name = "nested array"
let obj1 = clone(obj0)
obj1.o.n = 1
obj1.o.o.g = function g(a = 0, b = 0) { return a + b }
obj1.arr[1][1] = 3
obj1.d.setTime(+obj0.d + 60 * 1000)
obj1.arr.tint.is = "enumerable? no"
obj1.arr[0].name = "a nested arr"
defineProp(obj1, "s", { set(v) { this._s = v + 1 } })
defineProp(obj1.re, "multiline", { value: true })
console.log("\n\n" + "-".repeat(2 ** 6))
console.log(">:>: Test - Routinely")
console.log("obj0:\n ", JSON.stringify(obj0))
console.log("obj1:\n ", JSON.stringify(obj1))
console.log()
console.log("obj0:\n ", obj0)
console.log("obj1:\n ", obj1)
console.log()
console.log("obj0\n ",
".arr.tint:", obj0.arr.tint, "\n ",
".arr[0].name:", obj0.arr[0].name
)
console.log("obj1\n ",
".arr.tint:", obj1.arr.tint, "\n ",
".arr[0].name:", obj1.arr[0].name
)
console.log()
console.log("Accessor-type descriptor\n ",
"of obj0:", obj0.f.getAccessorStr(obj0), "\n ",
"of obj1:", obj1.f.getAccessorStr(obj1), "\n ",
"set (obj0 & obj1) .s :", obj0.s = obj1.s = 0, "\n ",
" → (obj0 , obj1) ._s:", obj0._s, ",", obj1._s
)
console.log("—— obj0 has not been interfered.")
console.log("\n\n" + "-".repeat(2 ** 6))
console.log(">:>: Test - More kinds of functions")
const fnsForTest = {
f(_) { return _ },
func: _ => _,
aFunc: async _ => _,
async function() { },
async asyncFunc() { },
aFn: async function () { },
*gen() { },
async *asyncGen() { },
aG1: async function* () { },
aG2: async function* gen() { },
*[Symbol.iterator]() { yield* Object.keys(this) }
}
console.log(Reflect.ownKeys(fnsForTest).map(k =>
`${String(k)}:
${fnsForTest[k].name}-->
${String(fnsForTest[k])}`
).join("\n"))
const normedFnsStr = `{
f: function f(_) { return _ },
func: _ => _,
aFunc: async _ => _,
function: async function() { },
asyncFunc: async function asyncFunc() { },
aFn: async function () { },
gen: function* gen() { },
asyncGen: async function* asyncGen() { },
aG1: async function* () { },
aG2: async function* gen() { },
[Symbol.iterator]: function* () { yield* Object.keys(this) }
}`
const copiedFnsForTest = clone(fnsForTest)
console.log("fnsForTest:", fnsForTest)
console.log("fnsForTest (copied):", copiedFnsForTest)
console.log("fnsForTest (normed str):", eval(`(${normedFnsStr})`))
console.log("Comparison of fnsForTest and its clone:",
Reflect.ownKeys(fnsForTest).map(k =>
[k, fnsForTest[k] === copiedFnsForTest[k]]
)
)
console.log("\n\n" + "-".repeat(2 ** 6))
console.log(">:>: Test - Circular structures")
obj0.o.r = {}
obj0.o.r.recursion = obj0.o
obj0.arr[1] = obj0.arr
obj1 = clone(obj0)
console.log("obj0:\n ", obj0)
console.log("obj1:\n ", obj1)
console.log("Clear obj0's recursion:",
obj0.o.r.recursion = null, obj0.arr[1] = 1
)
console.log(
"obj0\n ",
".o.r:", obj0.o.r, "\n ",
".arr:", obj0.arr
)
console.log(
"obj1\n ",
".o.r:", obj1.o.r, "\n ",
".arr:", obj1.arr
)
console.log("—— obj1 has not been interfered.")
console.log("\n\n" + "-".repeat(2 ** 6))
console.log(">:>: Test - Classes")
class Person {
constructor(name) {
this.name = name
}
}
class Boy extends Person { }
Boy.prototype.sex = "M"
const boy0 = new Boy
boy0.hobby = { sport: "spaceflight" }
const boy1 = clone(boy0)
boy1.hobby.sport = "superluminal flight"
boy0.name = "one"
boy1.name = "neo"
console.log("boy0:\n ", boy0)
console.log("boy1:\n ", boy1)
console.log("boy1's prototype === boy0's:",
Object.getPrototypeOf(boy1) === Object.getPrototypeOf(boy0)
)
工具书类
Object.create()| MDN对象.defineProperties()| MDN财产的可枚举性和所有权| MDNTypeError:循环对象值|MDN
使用的语言技巧
有条件地将道具添加到对象
有很多答案,但没有一个提到ECMAScript 5中的Object.create,它确实没有给您一个确切的副本,而是将源设置为新对象的原型。
因此,这不是问题的确切答案,但它是一个单行解决方案,因此很优雅。它最适合2种情况:
在这种继承有用的地方(duh!)源对象不会被修改,因此这两个对象之间的关系不成问题。
例子:
var foo = { a : 1 };
var bar = Object.create(foo);
foo.a; // 1
bar.a; // 1
foo.a = 2;
bar.a; // 2 - prototype changed
bar.a = 3;
foo.a; // Still 2, since setting bar.a makes it an "own" property
为什么我认为这种解决方案更优越?它是本地的,因此没有循环,没有递归。然而,较旧的浏览器将需要polyfill。
好的,这可能是浅层复制的最佳选择。If遵循了许多使用赋值的示例,但它也保留了继承和原型。它也很简单,适用于大多数类数组和对象,但有构造函数要求或只读财产的对象除外。但这意味着它对于TypedArrays、RegExp、Date、Maps、Set和Object版本的原语(Boolean、String等)失败得很惨。
function copy ( a ) { return Object.assign( new a.constructor, a ) }
其中a可以是任何Object或类构造的实例,但对于使用专门的getter和setter或具有构造函数要求的对象来说,它同样不可靠,但对于更简单的情况来说,它很难。它也能处理争论。
您也可以将其应用于原语以获得奇怪的结果,但是。。。除非它最终成为有用的黑客,谁在乎呢。
基本内置对象和数组的结果。。。
> a = { a: 'A', b: 'B', c: 'C', d: 'D' }
{ a: 'A', b: 'B', c: 'C', d: 'D' }
> b = copy( a )
{ a: 'A', b: 'B', c: 'C', d: 'D' }
> a = [1,2,3,4]
[ 1, 2, 3, 4 ]
> b = copy( a )
[ 1, 2, 3, 4 ]
由于平均get/setter、构造函数必需的参数或只读财产,以及对父亲的冒犯,因此失败。
> a = /\w+/g
/\w+/g
> b = copy( a ) // fails because source and flags are read-only
/(?:)/
> a = new Date ( '1/1/2001' )
2000-12-31T16:00:00.000Z
> b = copy( a ) // fails because Date using methods to get and set things
2017-02-04T14:44:13.990Z
> a = new Boolean( true )
[Boolean: true]
> b = copy( a ) // fails because of of sins against the father
[Boolean: false]
> a = new Number( 37 )
[Number: 37]
> b = copy( a ) // fails because of of sins against the father
[Number: 0]
> a = new String( 'four score and seven years ago our four fathers' )
[String: 'four score and seven years ago our four fathers']
> b = copy( a ) // fails because of of sins against the father
{ [String: ''] '0': 'f', '1': 'o', '2': 'u', '3': 'r', '4': ' ', '5': 's', '6': 'c', '7': 'o', '8': 'r', '9': 'e', '10': ' ', '11': 'a', '12': 'n', '13': 'd', '14': ' ', '15': 's', '16': 'e', '17': 'v', '18': 'e', '19': 'n', '20': ' ', '21': 'y', '22': 'e', '23': 'a', '24': 'r', '25': 's', '26': ' ', '27': 'a', '28': 'g', '29': 'o', '30': ' ', '31': 'o', '32': 'u', '33': 'r', '34': ' ', '35': 'f', '36': 'o', '37': 'u', '38': 'r', '39': ' ', '40': 'f', '41': 'a', '42': 't', '43': 'h', '44': 'e', '45': 'r', '46': 's' }
您可以克隆一个对象,并使用一行代码从上一个对象中删除任何引用。只需执行以下操作:
var obj1 = { text: 'moo1' };
var obj2 = Object.create(obj1); // Creates a new clone without references
obj2.text = 'moo2'; // Only updates obj2's text property
console.log(obj1, obj2); // Outputs: obj1: {text:'moo1'}, obj2: {text:'moo2'}
对于当前不支持Object.create的浏览器/引擎,可以使用以下polyfill:
// Polyfill Object.create if it does not exist
if (!Object.create) {
Object.create = function (o) {
var F = function () {};
F.prototype = o;
return new F();
};
}