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代码取自于underscore.js 1.8.3的isEqual函数。
做了一些小小的修改，主要是Function的比较修改。
自己也加了一些代码解读。
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>js中两个对象的比较</title> <script> /* 需求难点描述： 数组和对象，都能包含自身，还能包含其它类型。 所以数组之间的比较，要递归。 所以这块代码的设计是： 不能包含自身的，先比较。 然后是数组，对象比较。 特别要注意的是，对象的循环引用。 递归时，要记录递归的路径。 */ function isEqual(a, b) { var toString = Object.prototype.toString, object_keys = Object.keys, has = function(obj, key) { return obj != null && hasOwnProperty.call(obj, key); }; var isFunction = function(fn){ return toString.call(fn) == ‘[object Function]‘ ? true : false; }; 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). // 验证0===-0 if (a === b) return a !== 0 || 1 / a === 1 / b; // A strict comparison is necessary because `null == undefined`. // null // 验证null == undefined if (a == null || b == null) return a === b; // 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]‘: // function虽然是引用，但两个内容一样的funciton应该相等。 case ‘[object Function]‘: // 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 // 验证 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; } var areArrays = className === ‘[object Array]‘; if (!areArrays) { if (typeof a != ‘object‘ || typeof b != ‘object‘) return false; // Objects with different constructors are not equivalent, but `Object`s or `Array`s // from different frames are. var aCtor = a.constructor, bCtor = b.constructor; // 判断顺序 // 构造器一致 // 构造器为函数 // 拥有构造器属性 // Function instanceof Function == true // Object instanceof Object == true // Array instanceof Array == false if (aCtor !== bCtor && !(isFunction(aCtor) && aCtor instanceof aCtor && isFunction(bCtor) && bCtor instanceof bCtor) && (‘constructor‘ in a && ‘constructor‘ in b)) { 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`. // Initializing stack of traversed objects. // It‘s done here since we only need them for objects and arrays comparison. aStack = aStack || []; bStack = bStack || []; var length = aStack.length; while (length--) { // 递归才会走到这步 // Linear search. Performance is inversely proportional to the number of // unique nested structures. // 检测循环引用，参考用例如下 /* var a = { "str":"string", }; a["test"]=a; var b = { "str":"string", }; b["test"]=b; console.log (isEqual(a,b)); */ if (aStack[length] === a){ // 判断b的引用是否也循环，跳出循环引用这个坑 return bStack[length] === b; } } // Add the first object to the stack of traversed objects. // 递归压栈 aStack.push(a); bStack.push(b); // Recursively compare objects and arrays. if (areArrays) { // Compare array lengths to determine if a deep comparison is necessary. length = a.length; // 数组长度比较 if (length !== b.length) return false; // Deep compare the contents, ignoring non-numeric properties. // 递归比较 while (length--) { if (!eq(a[length], b[length], aStack, bStack)) return false; } } else { // Deep compare objects. // 把对象的属性们转换成一个数组 var keys = object_keys(a), key; length = keys.length; // Ensure that both objects contain the same number of properties before comparing deep equality. if (object_keys(b).length !== length) return false; while (length--) { // Deep compare each member key = keys[length]; // b也有a一样的key，则递归 if (!(has(b, key) && eq(a[key], b[key], aStack, bStack))) return false; } } // Remove the first object from the stack of traversed objects. // 递归出栈 aStack.pop(); bStack.pop(); return true; }; return eq(a,b); } var a = { "str":"ying", }; a["test"]=a; var b = { "str":"ying", }; b["test"]=a; console.log (isEqual(a,b)); </script> </head> <body> </body> </html>
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原文地址：http://www.cnblogs.com/samwu/p/4586217.html
