javascript的继承
来自 CasualJS，参考JavaScript高级程序设计(第2版)
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/** * Inheritance implementation for Javascript. */var inherit = function(childClass, parentClass) {var tmpConstructor = function() {};  tmpConstructor.prototype = parentClass.prototype;  childClass.superClass = parentClass.prototype;  childClass.prototype = new tmpConstructor();  childClass.prototype.constructor = childClass;        return  childClass;};