JavaScript中的对象比较 [英] Object comparison in JavaScript
问题描述
在JavaScript中比较对象的最佳方法是什么?
What is the best way to compare objects in JavaScript?
示例:
var user1 = {name : "nerd", org: "dev"};
var user2 = {name : "nerd", org: "dev"};
var eq = user1 == user2;
alert(eq); // gives false
我知道两个对象是相等的,如果他们指的是完全相同对象,但是有没有办法检查他们是否具有相同的属性值?
I know that two objects are equal if they refer to the exact same object, but is there a way to check if they have the same attributes' values?
以下方式适用于我, ?
The following way works for me, but is it the only possibility?
var eq = Object.toJSON(user1) == Object.toJSON(user2);
alert(eq); // gives true
推荐答案
不幸的是没有完美的方式,除非你使用 _proto _
递归并访问所有不可枚举的属性,但这只适用于Firefox。
Unfortunately there is no perfect way, unless you use _proto_
recursively and access all non-enumerable properties, but this works in Firefox only.
最好我可以做的是猜测使用场景。
So the best I can do is to guess usage scenarios.
在有没有方法和DOM节点的简单JSON样式对象时可以使用:
Works when you have simple JSON-style objects without methods and DOM nodes inside:
JSON.stringify(obj1) === JSON.stringify(obj2)
ORDER的属性是重要的,因此此方法将为以下对象返回false:
The ORDER of the properties IS IMPORTANT, so this method will return false for following objects:
x = {a: 1, b: 2};
y = {b: 2, a: 1};
2)
比较对象而不挖入原型,然后递归比较属性的投影,并比较构造函数。
2) Slow and more generic.
Compares objects without digging into prototypes, then compares properties' projections recursively, and also compares constructors.
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(好吧,他们的优先级很低,注意它们):
Known issues (well, they have very low priority, probably you'll never notice them):
- 具有不同原型结构但具有相同投影的对象
- 但指向不同的关闭
测试:测试通过 如何确定两个JavaScript对象的相等性? 。
Tests: passes tests are from How to determine equality for two JavaScript objects?.
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