javascript 判断对象是否相等

在Javascript中相等运算包括"==","==="全等，两者不同之处，不必多数，本篇文章我们将来讲述如何判断两个对象是否相等？ 你可能会认为，如果两个对象有相同的属性，以及它们的属性有相同的值，那么这两个对象就相等。那么下面我们通过一个实例来论证下：

var obj1 = {    name: "Benjamin",    sex : "male"}var obj2 = {    name: "Benjamin",    sex : "male"}//Outputs: falseconsole.log(obj1 == obj2);//Outputs: falseconsole.log(obj1 === obj2);

通过上面的例子可以看到，无论使用"=="还是"==="，都返回false。主要原因是基本类型string,number通过值来比较，而对象（Date,Array）及普通对象通过指针指向的内存中的地址来做比较。看下面一个例子：

var obj1 = {    name: "Benjamin",    sex : "male"};var obj2 = {    name: "Benjamin",    sex : "male"};var obj3 = obj1;//Outputs: trueconsole.log(obj1 == obj3);//Outputs: trueconsole.log(obj1 === obj3);//Outputs: falseconsole.log(obj2 == obj3);//Outputs: falseconsole.log(obj2 === obj3);

上例返回true，是因为obj1和ob3的指针指向了内存中的同一个地址。和面向对象的语言（Java/C++）中值传递和引用传递的概念相似。 因为，如果你想判断两个对象是否相等，你必须清晰，你是想判断两个对象的属性是否相同，还是属性对应的值是否相同，还是怎样？如果你判断两个对象的值是否相等，可以像下面这样：

function isObjectValueEqual(a, b) {    // Of course, we can do it use for in     // Create arrays of PRoperty names    var aProps = Object.getOwnPropertyNames(a);    var bProps = Object.getOwnPropertyNames(b);    // If number of properties is different,    // objects are not equivalent    if (aProps.length != bProps.length) {        return false;    }    for (var i = 0; i < aProps.length; i++) {        var propName = aProps[i];        // If values of same property are not equal,        // objects are not equivalent        if (a[propName] !== b[propName]) {            return false;        }    }    // If we made it this far, objects    // are considered equivalent    return true;}var obj1 = {    name: "Benjamin",    sex : "male"};var obj2 = {    name: "Benjamin",    sex : "male"};//Outputs: trueconsole.log(isObjectValueEqual(obj1, obj2));

正如你所看到的，检查对象的“值相等”我们基本上是要遍历的对象的每个属性，看看它们是否相等。虽然这个简单的实现适用于我们的例子中，有很多情况下，它是不能处理。例如： 1) 如果该属性值之一本身就是一个对象吗？ 2) 如果属性值中的一个是NaN（在JavaScript中，是不是等于自己唯一的价值？） 3) 如果一个属性的值为undefined，而另一个对象没有这个属性（因而计算结果为不确定？） 检查对象的“值相等”的一个强大的方法，最好是依靠完善的测试库，涵盖了各种边界情况。Underscore和Lo-Dash有一个名为_.isEqual()方法，用来比较好的处理深度对象的比较。您可以使用它们像这样：

// Outputs: trueconsole.log(_.isEqual(obj1, obj2));

最后附上Underscore中isEqual的部分源码：

  // Internal recursive comparison function for `isEqual`.  var eq = function(a, b, aStack, bStack) {    // Identical objects are equal. `0 === -0`, but they aren't identical.    // See the [Harmony `egal` proposal](http://wiki.ecmascript.org/doku.php?id=harmony:egal).    if (a === b) return a !== 0 || 1 / a === 1 / b;    // A strict comparison is necessary because `null == undefined`.    if (a == null || b == null) return a === b;    // Unwrap any wrapped objects.    if (a instanceof _) a = a._wrapped;    if (b instanceof _) b = b._wrapped;    // Compare `[[Class]]` names.    var className = toString.call(a);    if (className !== toString.call(b)) return false;    switch (className) {      // Strings, numbers, regular expressions, dates, and booleans are compared by value.      case '[object RegExp]':      // RegExps are coerced to strings for comparison (Note: '' + /a/i === '/a/i')      case '[object String]':        // Primitives and their corresponding object wrappers are equivalent; thus, `"5"` is        // equivalent to `new String("5")`.        return '' + a === '' + b;      case '[object Number]':        // `NaN`s are equivalent, but non-reflexive.        // Object(NaN) is equivalent to NaN        if (+a !== +a) return +b !== +b;        // An `egal` comparison is performed for other numeric values.        return +a === 0 ? 1 / +a === 1 / b : +a === +b;      case '[object Date]':      case '[object Boolean]':        // Coerce dates and booleans to numeric primitive values. Dates are compared by their        // millisecond representations. Note that invalid dates with millisecond representations        // of `NaN` are not equivalent.        return +a === +b;    }    if (typeof a != 'object' || typeof b != 'object') return false;    // Assume equality for cyclic structures. The algorithm for detecting cyclic    // structures is adapted from ES 5.1 section 15.12.3, abstract Operation `JO`.    var length = aStack.length;    while (length--) {      // Linear search. Performance is inversely proportional to the number of      // unique nested structures.      if (aStack[length] === a) return bStack[length] === b;    }    // Objects with different constructors are not equivalent, but `Object`s    // from different frames are.    var aCtor = a.constructor, bCtor = b.constructor;    if (      aCtor !== bCtor &&      // Handle Object.create(x) cases      'constructor' in a && 'constructor' in b &&      !(_.isFunction(aCtor) && aCtor instanceof aCtor &&        _.isFunction(bCtor) && bCtor instanceof bCtor)    ) {      return false;    }    // Add the first object to the stack of traversed objects.    aStack.push(a);    bStack.push(b);    var size, result;    // Recursively compare objects and arrays.    if (className === '[object Array]') {      // Compare array lengths to determine if a deep comparison is necessary.      size = a.length;      result = size === b.length;      if (result) {        // Deep compare the contents, ignoring non-numeric properties.        while (size--) {          if (!(result = eq(a[size], b[size], aStack, bStack))) break;        }      }    } else {      // Deep compare objects.      var keys = _.keys(a), key;      size = keys.length;      // Ensure that both objects contain the same number of properties before comparing deep equality.      result = _.keys(b).length === size;      if (result) {        while (size--) {          // Deep compare each member          key = keys[size];          if (!(result = _.has(b, key) && eq(a[key], b[key], aStack, bStack))) break;        }      }    }    // Remove the first object from the stack of traversed objects.    aStack.pop();    bStack.pop();    return result;  };  // Perform a deep comparison to check if two objects are equal.  _.isEqual = function(a, b) {    return eq(a, b, [], []);  };

感谢您的阅读，希望此篇文章对您有所帮助，文中不足之处欢迎批评斧正。

转载声明：

本文标题：Javascript 判断对象是否相等

本文链接：http://www.zuojj.com/archives/775.html，转载请注明转自Benjamin-专注前端开发和用户体验