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function A(){ this.name = "a"; } A.prototype = { M:function(){ return 2; } } var B = function(){} var a = new A(); var b = new B(); console.log(A.prototype.constructor);//Object console.log(a.__proto__ == A.prototype);//true console.log(a.__proto__.constructor);//Object console.log(b.__proto__.constructor == B);//true