严格相等运算符将告诉您两个对象类型是否相等。然而,是否有一种方法来判断两个对象是否相等,就像Java中的哈希码值一样?

堆栈溢出问题JavaScript中有hashCode函数吗?类似于这个问题,但需要一个更学术的答案。上面的场景说明了为什么有必要有一个,我想知道是否有等效的解决方案。


当前回答

我写这个方法只是为了确保数组和对象都能被清晰地比较。

这应该也能做到!:)

public class Objects {
    /**
     * Checks whether a value is of type Object
     * @param value the value
     */
    public static isObject = (value: any): boolean => {
        return value === Object(value) && Object.prototype.toString.call(value) !== '[object Array]'
    }

    /**
     * Checks whether a value is of type Array
     * @param value the value
     */
    public static isArray = (value: any): boolean => {
        return Object.prototype.toString.call(value) === '[object Array]' && !Objects.isObject(value)
    }

    /**
     * Check whether two values are equal
     */
    public static isEqual = (objectA: any, objectB: any) => {
        // Objects
        if (Objects.isObject(objectA) && !Objects.isObject(objectB)) {
            return false
        }
        else if (!Objects.isObject(objectA) && Objects.isObject(objectB)) {
            return false
        }
        // Arrays
        else if (Objects.isArray(objectA) && !Objects.isArray(objectB)) {
            return false
        }
        else if (!Objects.isArray(objectA) && Objects.isArray(objectB)) {
            return false
        }
        // Primitives
        else if (!Objects.isArray(objectA) && !Objects.isObject(objectA)) {
            return objectA === objectB
        }
        // Object or array
        else {
            const compareObject = (objectA: any, objectB: any): boolean => {
                if (Object.keys(objectA).length !== Object.keys(objectB).length) return false

                for (const propertyName of Object.keys(objectA)) {
                    const valueA = objectA[propertyName]
                    const valueB = objectB[propertyName]

                    if (!Objects.isEqual(valueA, valueB)) {
                        return false
                    }
                }

                return true
            }
            const compareArray = (arrayA: any[], arrayB: any[]): boolean => {
                if (arrayA.length !== arrayB.length) return false

                for (const index in arrayA) {
                    const valueA = arrayA[index]
                    const valueB = arrayB[index]

                    if (!Objects.isEqual(valueA, valueB)) {
                        return false
                    }
                }

                return true
            }
            if (Objects.isObject(objectA)) {
                return compareObject(objectA, objectB)
            } else {
                return compareArray(objectA, objectB)
            }
        }
    }
}

其他回答

这取决于你对平等的定义。因此,作为类的开发人员,要由您来定义它们的相等性。

有时会使用一种情况,如果两个实例指向内存中的相同位置,则认为它们是“相等的”,但这并不总是您想要的。例如,如果我有一个Person类,如果两个Person对象具有相同的Last Name、First Name和Social Security Number(即使它们指向内存中的不同位置),我可能会认为它们是“相等的”。

另一方面,我们不能简单地说两个对象是相等的,如果它们的每个成员的值都相同,因为,有时,你并不想这样。换句话说,对于每个类,由类开发人员定义组成对象“标识”的成员并开发适当的相等操作符(通过重载==操作符或Equals方法)。

Saying that two objects are equal if they have the same hash is one way out. However you then have to wonder how the hash is calculated for each instance. Going back to the Person example above, we could use this system if the hash was calculated by looking at the values of the First Name, Last Name, and Social Security Number fields. On top of that, we are then relying on the quality of the hashing method (that's a huge topic on its own, but suffice it to say that not all hashes are created equal, and bad hashing methods can lead to more collisions, which in this case would return false matches).

纯JS方法:我的答案是基于生成一个返回相同值的字符串,无论属性顺序是否相同。设置对象可用于切换大小写和空白是否重要。(为了避免失去焦点,我没有包括那些支持函数,或者我猜应该在任何实用程序集中的isObject。)

这里也没有显示,但为了减少字符串比较时间,如果对象很大,你想加快比较,你也可以散列字符串和比较子字符串;这只适用于非常大的对象(当然也有很小的机会出现错误的相等)。

然后你可以比较genObjStr(obj1) ?= genObjStr(obj2)

function genObjStr(obj, settings) {
// Generate a string that corresponds to an object guarenteed to be the same str even if
// the object have different ordering. The string would largely be used for comparison purposes

var settings = settings||{};
var doStripWhiteSpace = defTrue(settings.doStripWhiteSpace);
var doSetLowerCase = settings.doSetLowerCase||false;

if(isArray(obj)) {
    var vals = [];
    for(var i = 0; i < obj.length; ++i) {
        vals.push(genObjStr(obj[i], settings));
    }
    vals = arraySort(vals);
    return vals.join(`,`);

} else if(isObject(obj)) {

    var keys = Object.keys(obj);
    keys = arraySort(keys);

    var vals = [];
    for(var key of keys) {
        
        var value = obj[key];
        
        value = genObjStr(value, settings);

        if(doStripWhiteSpace) {
            key = removeWhitespace(key);
            var value = removeWhitespace(value);
        };
        if(doSetLowerCase) {
            key = key.toLowerCase();
            value = value.toLowerCase();
        }

        vals.push(value);
    }
    var str = JSON.stringify({keys: keys, vals: vals});
    return str
} else {
    if(doStripWhiteSpace) {
        obj = removeWhitespace(obj);
    };
    if(doSetLowerCase) {
        obj = obj.toLowerCase();
    }
    return obj
}

}

var obj1 = {foo: 123, bar: `Test`};
var obj2 = {bar: `Test`, foo: 123};

console.log(genObjStr(obj1) == genObjStr(obj1))

EDIT: This method is quite flawed, and is rife with its own issues. I don't recommend it, and would appreciate some down-votes! It is problematic because 1) Some things can not be compared (i.e. functions) because they can not be serialized, 2) It isn't a very fast method of comparing, 3) It has ordering issues, 4) It can have collision issues/false positives if not properly implemented, 5) It can't check for "exactness" (===), and instead is based of value equality, which is oftentimes not what is desired in a comparison method.

这个问题的一个简单解决方案是对JSON字符串进行排序(每个字符),但很多人没有意识到这一点。这通常也比这里提到的其他解决方案更快:

function areEqual(obj1, obj2) {
    var a = JSON.stringify(obj1), b = JSON.stringify(obj2);
    if (!a) a = '';
    if (!b) b = '';
    return (a.split('').sort().join('') == b.split('').sort().join(''));
}

关于这个方法的另一个有用的事情是,您可以通过向JSON传递一个“replace”函数来筛选比较。stringify函数(https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify#Example_of_using_replacer_parameter)。下面只比较所有命名为“derp”的对象键:

function areEqual(obj1, obj2, filter) {
    var a = JSON.stringify(obj1, filter), b = JSON.stringify(obj2, filter);
    if (!a) a = '';
    if (!b) b = '';
    return (a.split('').sort().join('') == b.split('').sort().join(''));
}
var equal = areEqual(obj1, obj2, function(key, value) {
    return (key === 'derp') ? value : undefined;
});

我知道这有点老了,但我想添加一个解决方案,我想出了这个问题。 我有一个对象,我想知道它的数据什么时候改变。类似于Object。我所做的是:

function checkObjects(obj,obj2){
   var values = [];
   var keys = [];
   keys = Object.keys(obj);
   keys.forEach(function(key){
      values.push(key);
   });
   var values2 = [];
   var keys2 = [];
   keys2 = Object.keys(obj2);
   keys2.forEach(function(key){
      values2.push(key);
   });
   return (values == values2 && keys == keys2)
}

这里可以复制并创建另一组数组来比较值和键。 这很简单,因为它们现在是数组,如果对象大小不同将返回false。

我看到了意大利式的代码答案。 不使用任何第三方的lib,这是非常容易的。

首先,按键对两个对象进行排序。

let objectOne = { hey, you }
let objectTwo = { you, hey }

// If you really wanted you could make this recursive for deep sort.
const sortObjectByKeyname = (objectToSort) => {
    return Object.keys(objectToSort).sort().reduce((r, k) => (r[k] = objectToSort[k], r), {});
}

let objectOne = sortObjectByKeyname(objectOne)
let objectTwo = sortObjectByKeyname(objectTwo)

然后简单地使用字符串来比较它们。

JSON.stringify(objectOne) === JSON.stringify(objectTwo)