在JavaScript中，比较对象的最佳方法是什么？
示例：
var user1 = {name : "nerd", org: "dev"};
var user2 = {name : "nerd", org: "dev"};
var eq = user1 == user2;
alert(eq); // gives false
var eq = Object.toJSON(user1) == Object.toJSON(user2);
alert(eq); // gives true
很遗憾，除非您递归使用_proto_并访问所有不可枚举属性，否则没有完美的方法，但这仅适用于Firefox。
因此，我能做的最好的事情就是猜测使用场景。
适用于没有方法和DOM节点的简单JSON风格对象：
JSON.stringify(obj1) === JSON.stringify(obj2)
x = {a: 1, b: 2};
y = {b: 2, a: 1};
比较对象时不深入原型，然后递归地比较属性的投影，并比较构造函数。
这几乎是正确的算法：
function deepCompare () {
var i, l, leftChain, rightChain;
function compare2Objects (x, y) {
var p;
// remember that NaN === NaN returns false
// and isNaN(undefined) returns true
if (isNaN(x) && isNaN(y) && typeof x === 'number' && typeof y === 'number') {
return true;
}
// Compare primitives and functions.
// Check if both arguments link to the same object.
// Especially useful on the step where we compare prototypes
if (x === y) {
return true;
}
// Works in case when functions are created in constructor.
// Comparing dates is a common scenario. Another built-ins?
// We can even handle functions passed across iframes
if ((typeof x === 'function' && typeof y === 'function') ||
(x instanceof Date && y instanceof Date) ||
(x instanceof RegExp && y instanceof RegExp) ||
(x instanceof String && y instanceof String) ||
(x instanceof Number && y instanceof Number)) {
return x.toString() === y.toString();
}
// At last checking prototypes as good as we can
if (!(x instanceof Object && y instanceof Object)) {
return false;
}
if (x.isPrototypeOf(y) || y.isPrototypeOf(x)) {
return false;
}
if (x.constructor !== y.constructor) {
return false;
}
if (x.prototype !== y.prototype) {
return false;
}
// Check for infinitive linking loops
if (leftChain.indexOf(x) > -1 || rightChain.indexOf(y) > -1) {
return false;
}
// Quick checking of one object being a subset of another.
// todo: cache the structure of arguments[0] for performance
for (p in y) {
if (y.hasOwnProperty(p) !== x.hasOwnProperty(p)) {
return false;
}
else if (typeof y[p] !== typeof x[p]) {
return false;
}
}
for (p in x) {
if (y.hasOwnProperty(p) !== x.hasOwnProperty(p)) {
return false;
}
else if (typeof y[p] !== typeof x[p]) {
return false;
}
switch (typeof (x[p])) {
case 'object':
case 'function':
leftChain.push(x);
rightChain.push(y);
if (!compare2Objects (x[p], y[p])) {
return false;
}
leftChain.pop();
rightChain.pop();
break;
default:
if (x[p] !== y[p]) {
return false;
}
break;
}
}
return true;
}
if (arguments.length < 1) {
return true; //Die silently? Don't know how to handle such case, please help...
// throw "Need two or more arguments to compare";
}
for (i = 1, l = arguments.length; i < l; i++) {
leftChain = []; //Todo: this can be cached
rightChain = [];
if (!compare2Objects(arguments[0], arguments[i])) {
return false;
}
}
return true;
}
已知问题（嗯，它们的优先级非常低，可能你永远不会注意到）：
测试： 通过测试来自于如何确定两个JavaScript对象的相等性？。
in运算符而不是typeof可以避免这种情况：p in x。通过字符串值比较函数非常不可靠，除了通常函数分解失败的原因外，由于闭包，拥有相同代码但行为非常不同的两个函数也很常见。例如，任何由jQuery的$.proxy或Prototype的Function#bind创建的函数。我建议仅使用函数标识进行比较。 - bobince===，因为{ a: 5 }和{ a: "5.0" }并不相等，或者它们是相等的吗？ - Crozinif(!someObject.hasOwnProperty(key)) continue;，则会破坏 for(var key in someObject) 的功能。 - ThiefMasterthis[p] === x[p]。 - Eamon Nerbonnefalse，也可能不会。没有任何保证。这就是为什么我们不使用 JSON.stringify 来比较对象。因为属性的顺序没有保证。 - user2437417这是我的ES3注释解决方案（代码后面有详细信息）：
function object_equals( x, y ) {
if ( x === y ) return true;
// if both x and y are null or undefined and exactly the same
if ( ! ( x instanceof Object ) || ! ( y instanceof Object ) ) return false;
// if they are not strictly equal, they both need to be Objects
if ( x.constructor !== y.constructor ) return false;
// they must have the exact same prototype chain, the closest we can do is
// test there constructor.
for ( var p in x ) {
if ( ! x.hasOwnProperty( p ) ) continue;
// other properties were tested using x.constructor === y.constructor
if ( ! y.hasOwnProperty( p ) ) return false;
// allows to compare x[ p ] and y[ p ] when set to undefined
if ( x[ p ] === y[ p ] ) continue;
// if they have the same strict value or identity then they are equal
if ( typeof( x[ p ] ) !== "object" ) return false;
// Numbers, Strings, Functions, Booleans must be strictly equal
if ( ! object_equals( x[ p ], y[ p ] ) ) return false;
// Objects and Arrays must be tested recursively
}
for ( p in y )
if ( y.hasOwnProperty( p ) && ! x.hasOwnProperty( p ) )
return false;
// allows x[ p ] to be set to undefined
return true;
}
总的来说，这段代码只有16行（不包括注释）就处理了大多数边角情况。
Utils.compareObjects = function(o1, o2){
for(var p in o1){
if(o1.hasOwnProperty(p)){
if(o1[p] !== o2[p]){
return false;
}
}
}
for(var p in o2){
if(o2.hasOwnProperty(p)){
if(o1[p] !== o2[p]){
return false;
}
}
}
return true;
};
比较仅限于单级对象的简单方法。
这绝不是唯一的方法 - 您可以原型化一个方法（此处针对Object，但我绝不建议在实际代码中使用Object）来复制C＃/Java风格的比较方法。
编辑，由于似乎需要提供一个通用示例：
Object.prototype.equals = function(x)
{
for(p in this)
{
switch(typeof(this[p]))
{
case 'object':
if (!this[p].equals(x[p])) { return false }; break;
case 'function':
if (typeof(x[p])=='undefined' || (p != 'equals' && this[p].toString() != x[p].toString())) { return false; }; break;
default:
if (this[p] != x[p]) { return false; }
}
}
for(p in x)
{
if(typeof(this[p])=='undefined') {return false;}
}
return true;
}
请注意，使用toString()方法进行测试绝对不够好，但是一个可以接受的方法非常困难，因为空格是否具有意义，别提同义词方法和以不同实现产生相同结果的方法了。 还有一般情况下原型与对象之间的问题。
function unwrapStringOrNumber(obj) {
return (obj instanceof Number || obj instanceof String
? obj.valueOf()
: obj);
}
function areEquivalent(a, b) {
a = unwrapStringOrNumber(a);
b = unwrapStringOrNumber(b);
if (a === b) return true; //e.g. a and b both null
if (a === null || b === null || typeof (a) !== typeof (b)) return false;
if (a instanceof Date)
return b instanceof Date && a.valueOf() === b.valueOf();
if (typeof (a) !== "object")
return a == b; //for boolean, number, string, xml
var newA = (a.areEquivalent_Eq_91_2_34 === undefined),
newB = (b.areEquivalent_Eq_91_2_34 === undefined);
try {
if (newA) a.areEquivalent_Eq_91_2_34 = [];
else if (a.areEquivalent_Eq_91_2_34.some(
function (other) { return other === b; })) return true;
if (newB) b.areEquivalent_Eq_91_2_34 = [];
else if (b.areEquivalent_Eq_91_2_34.some(
function (other) { return other === a; })) return true;
a.areEquivalent_Eq_91_2_34.push(b);
b.areEquivalent_Eq_91_2_34.push(a);
var tmp = {};
for (var prop in a)
if(prop != "areEquivalent_Eq_91_2_34")
tmp[prop] = null;
for (var prop in b)
if (prop != "areEquivalent_Eq_91_2_34")
tmp[prop] = null;
for (var prop in tmp)
if (!areEquivalent(a[prop], b[prop]))
return false;
return true;
} finally {
if (newA) delete a.areEquivalent_Eq_91_2_34;
if (newB) delete b.areEquivalent_Eq_91_2_34;
}
}
我编写了这段对象比较的代码，它似乎有效。检查断言：
function countProps(obj) {
var count = 0;
for (k in obj) {
if (obj.hasOwnProperty(k)) {
count++;
}
}
return count;
};
function objectEquals(v1, v2) {
if (typeof(v1) !== typeof(v2)) {
return false;
}
if (typeof(v1) === "function") {
return v1.toString() === v2.toString();
}
if (v1 instanceof Object && v2 instanceof Object) {
if (countProps(v1) !== countProps(v2)) {
return false;
}
var r = true;
for (k in v1) {
r = objectEquals(v1[k], v2[k]);
if (!r) {
return false;
}
}
return true;
} else {
return v1 === v2;
}
}
assert.isTrue(objectEquals(null,null));
assert.isFalse(objectEquals(null,undefined));
assert.isTrue(objectEquals("hi","hi"));
assert.isTrue(objectEquals(5,5));
assert.isFalse(objectEquals(5,10));
assert.isTrue(objectEquals([],[]));
assert.isTrue(objectEquals([1,2],[1,2]));
assert.isFalse(objectEquals([1,2],[2,1]));
assert.isFalse(objectEquals([1,2],[1,2,3]));
assert.isTrue(objectEquals({},{}));
assert.isTrue(objectEquals({a:1,b:2},{a:1,b:2}));
assert.isTrue(objectEquals({a:1,b:2},{b:2,a:1}));
assert.isFalse(objectEquals({a:1,b:2},{a:1,b:3}));
assert.isTrue(objectEquals({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}},{1:{name:"mhc",age:28}, 2:{name:"arb",age:26}}));
assert.isFalse(objectEquals({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}},{1:{name:"mhc",age:28}, 2:{name:"arb",age:27}}));
assert.isTrue(objectEquals(function(x){return x;},function(x){return x;}));
assert.isFalse(objectEquals(function(x){return x;},function(y){return y+2;}));
我稍微修改了上面的代码。对我来说，0 !== false和null !== undefined。如果您不需要这样严格的检查，请在代码中的"this[p] !== x[p]"中删除一个"="符号。
Object.prototype.equals = function(x){
for (var p in this) {
if(typeof(this[p]) !== typeof(x[p])) return false;
if((this[p]===null) !== (x[p]===null)) return false;
switch (typeof(this[p])) {
case 'undefined':
if (typeof(x[p]) != 'undefined') return false;
break;
case 'object':
if(this[p]!==null && x[p]!==null && (this[p].constructor.toString() !== x[p].constructor.toString() || !this[p].equals(x[p]))) return false;
break;
case 'function':
if (p != 'equals' && this[p].toString() != x[p].toString()) return false;
break;
default:
if (this[p] !== x[p]) return false;
}
}
return true;
}
接下来，我对以下对象进行了测试：
var a = {a: 'text', b:[0,1]};
var b = {a: 'text', b:[0,1]};
var c = {a: 'text', b: 0};
var d = {a: 'text', b: false};
var e = {a: 'text', b:[1,0]};
var f = {a: 'text', b:[1,0], f: function(){ this.f = this.b; }};
var g = {a: 'text', b:[1,0], f: function(){ this.f = this.b; }};
var h = {a: 'text', b:[1,0], f: function(){ this.a = this.b; }};
var i = {
a: 'text',
c: {
b: [1, 0],
f: function(){
this.a = this.b;
}
}
};
var j = {
a: 'text',
c: {
b: [1, 0],
f: function(){
this.a = this.b;
}
}
};
var k = {a: 'text', b: null};
var l = {a: 'text', b: undefined};
a==b 预期结果为true；实际返回结果为true
a==c 预期结果为false；实际返回结果为false
c==d 预期结果为false；实际返回结果为false
a==e 预期结果为false；实际返回结果为false
f==g 预期结果为true；实际返回结果为true
h==g 预期结果为false；实际返回结果为false
i==j 预期结果为true；实际返回结果为true
d==k 预期结果为false；实际返回结果为false
k==l 预期结果为false；实际返回结果为false
这是我的版本，基本上整合了这个主题中的大部分内容（测试用例也是如此）：
Object.defineProperty(Object.prototype, "equals", {
enumerable: false,
value: function (obj) {
var p;
if (this === obj) {
return true;
}
// some checks for native types first
// function and sring
if (typeof(this) === "function" || typeof(this) === "string" || this instanceof String) {
return this.toString() === obj.toString();
}
// number
if (this instanceof Number || typeof(this) === "number") {
if (obj instanceof Number || typeof(obj) === "number") {
return this.valueOf() === obj.valueOf();
}
return false;
}
// null.equals(null) and undefined.equals(undefined) do not inherit from the
// Object.prototype so we can return false when they are passed as obj
if (typeof(this) !== typeof(obj) || obj === null || typeof(obj) === "undefined") {
return false;
}
function sort (o) {
var result = {};
if (typeof o !== "object") {
return o;
}
Object.keys(o).sort().forEach(function (key) {
result[key] = sort(o[key]);
});
return result;
}
if (typeof(this) === "object") {
if (Array.isArray(this)) { // check on arrays
return JSON.stringify(this) === JSON.stringify(obj);
} else { // anyway objects
for (p in this) {
if (typeof(this[p]) !== typeof(obj[p])) {
return false;
}
if ((this[p] === null) !== (obj[p] === null)) {
return false;
}
switch (typeof(this[p])) {
case 'undefined':
if (typeof(obj[p]) !== 'undefined') {
return false;
}
break;
case 'object':
if (this[p] !== null
&& obj[p] !== null
&& (this[p].constructor.toString() !== obj[p].constructor.toString()
|| !this[p].equals(obj[p]))) {
return false;
}
break;
case 'function':
if (this[p].toString() !== obj[p].toString()) {
return false;
}
break;
default:
if (this[p] !== obj[p]) {
return false;
}
}
};
}
}
// at least check them with JSON
return JSON.stringify(sort(this)) === JSON.stringify(sort(obj));
}
});
这是我的测试用例:
assertFalse({}.equals(null));
assertFalse({}.equals(undefined));
assertTrue("String", "hi".equals("hi"));
assertTrue("Number", new Number(5).equals(5));
assertFalse("Number", new Number(5).equals(10));
assertFalse("Number+String", new Number(1).equals("1"));
assertTrue([].equals([]));
assertTrue([1,2].equals([1,2]));
assertFalse([1,2].equals([2,1]));
assertFalse([1,2].equals([1,2,3]));
assertTrue(new Date("2011-03-31").equals(new Date("2011-03-31")));
assertFalse(new Date("2011-03-31").equals(new Date("1970-01-01")));
assertTrue({}.equals({}));
assertTrue({a:1,b:2}.equals({a:1,b:2}));
assertTrue({a:1,b:2}.equals({b:2,a:1}));
assertFalse({a:1,b:2}.equals({a:1,b:3}));
assertTrue({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}}.equals({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}}));
assertFalse({1:{name:"mhc",age:28}, 2:{name:"arb",age:26}}.equals({1:{name:"mhc",age:28}, 2:{name:"arb",age:27}}));
assertTrue("Function", (function(x){return x;}).equals(function(x){return x;}));
assertFalse("Function", (function(x){return x;}).equals(function(y){return y+2;}));
var a = {a: 'text', b:[0,1]};
var b = {a: 'text', b:[0,1]};
var c = {a: 'text', b: 0};
var d = {a: 'text', b: false};
var e = {a: 'text', b:[1,0]};
var f = {a: 'text', b:[1,0], f: function(){ this.f = this.b; }};
var g = {a: 'text', b:[1,0], f: function(){ this.f = this.b; }};
var h = {a: 'text', b:[1,0], f: function(){ this.a = this.b; }};
var i = {
a: 'text',
c: {
b: [1, 0],
f: function(){
this.a = this.b;
}
}
};
var j = {
a: 'text',
c: {
b: [1, 0],
f: function(){
this.a = this.b;
}
}
};
var k = {a: 'text', b: null};
var l = {a: 'text', b: undefined};
assertTrue(a.equals(b));
assertFalse(a.equals(c));
assertFalse(c.equals(d));
assertFalse(a.equals(e));
assertTrue(f.equals(g));
assertFalse(h.equals(g));
assertTrue(i.equals(j));
assertFalse(d.equals(k));
assertFalse(k.equals(l));
Object.prototype.equals = function(b) {
var a = this;
for(i in a) {
if(typeof b[i] == 'undefined') {
return false;
}
if(typeof b[i] == 'object') {
if(!b[i].equals(a[i])) {
return false;
}
}
if(b[i] != a[i]) {
return false;
}
}
for(i in b) {
if(typeof a[i] == 'undefined') {
return false;
}
if(typeof a[i] == 'object') {
if(!a[i].equals(b[i])) {
return false;
}
}
if(a[i] != b[i]) {
return false;
}
}
return true;
}
var a = {foo:'bar', bar: {blub:'bla'}};
var b = {foo:'bar', bar: {blub:'blob'}};
alert(a.equals(b)); // alert's a false
如果您想明确检查方法，可以使用method.toSource()或method.toString()方法。
toSource已经被弃用，请勿使用。 - hazer_hazer
equal()实现的测试套件。文档中的讨论也十分详细。 - flowisEqual方法恰好符合你的需求。 - Adam Fraser_.isEqual(obj1, obj2)。 - Sai Ram