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
如果你对一个浅拷贝没有问题,underscore.js库有一个克隆方法。
y = _.clone(x);
或者你可以像
copiedObject = _.extend({},originalObject);
其他回答
(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
//
// creates 'clone' method on context object
//
// var
// clon = Object.clone( anyValue );
//
!((function (propertyName, definition) {
this[propertyName] = definition();
}).call(
Object,
"clone",
function () {
function isfn(fn) {
return typeof fn === "function";
}
function isobj(o) {
return o === Object(o);
}
function isarray(o) {
return Object.prototype.toString.call(o) === "[object Array]";
}
function fnclon(fn) {
return function () {
fn.apply(this, arguments);
};
}
function owns(obj, p) {
return obj.hasOwnProperty(p);
}
function isemptyobj(obj) {
for (var p in obj) {
return false;
}
return true;
}
function isObject(o) {
return Object.prototype.toString.call(o) === "[object Object]";
}
return function (input) {
if (isfn(input)) {
return fnclon(input);
} else if (isobj(input)) {
var cloned = {};
for (var p in input) {
owns(Object.prototype, p)
|| (
isfn(input[p])
&& ( cloned[p] = function () { return input[p].apply(input, arguments); } )
|| ( cloned[p] = input[p] )
);
}
if (isarray(input)) {
cloned.length = input.length;
"concat every filter forEach indexOf join lastIndexOf map pop push reduce reduceRight reverse shift slice some sort splice toLocaleString toString unshift"
.split(" ")
.forEach(
function (methodName) {
isfn( Array.prototype[methodName] )
&& (
cloned[methodName] =
function () {
return Array.prototype[methodName].apply(cloned, arguments);
}
);
}
);
}
return isemptyobj(cloned)
? (
isObject(input)
? cloned
: input
)
: cloned;
} else {
return input;
}
};
}
));
//
在一行代码中克隆Javascript对象的优雅方法
Object.assign方法是ECMAScript 2015(ES6)标准的一部分,它完全符合您的需要。
var clone = Object.assign({}, obj);
assign()方法用于将所有可枚举自身财产的值从一个或多个源对象复制到目标对象。
阅读更多。。。
支持旧浏览器的polyfill:
if (!Object.assign) {
Object.defineProperty(Object, 'assign', {
enumerable: false,
configurable: true,
writable: true,
value: function(target) {
'use strict';
if (target === undefined || target === null) {
throw new TypeError('Cannot convert first argument to object');
}
var to = Object(target);
for (var i = 1; i < arguments.length; i++) {
var nextSource = arguments[i];
if (nextSource === undefined || nextSource === null) {
continue;
}
nextSource = Object(nextSource);
var keysArray = Object.keys(nextSource);
for (var nextIndex = 0, len = keysArray.length; nextIndex < len; nextIndex++) {
var nextKey = keysArray[nextIndex];
var desc = Object.getOwnPropertyDescriptor(nextSource, nextKey);
if (desc !== undefined && desc.enumerable) {
to[nextKey] = nextSource[nextKey];
}
}
}
return to;
}
});
}
如果您的对象是类(例如。https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes):
var copiedObject = jQuery.extend(true, {}, originalObject);
copiedObject.__proto__ = originalObject.__proto__;
然后在copiedObject中,您有一个originalObject类及其所有方法的深度复制实例。
我不知道这在哪些情况下不起作用,但它给了我一个数组的副本。我觉得它很可爱:)希望它有帮助
copiedArr = origArr.filter(function(x){return true})