1.①__proto__ and the object constructor property is unique; ② prototype property is a unique function, because function is also an object, so also has the function __proto__ and constructor property.
2 .__ role proto__ property is that when accessing properties of an object, if the object is inside this property does not exist, then it will go to that object __proto__ attribute points (parent) where to find, been looking for, null __proto__ property until the end and then returns undefined, the objects connected by this link __proto__ property which we called prototype chain.
3.prototype role is to make the property function instantiated object who can find common properties and methods that a1 .__ proto__ === A.prototype.
4.constructor meaning attribute is a pointer to the object's constructor function, all functions (in this case as the subject) constructor final point Function ().
function A() {}
A.prototype.name = '1';
where a1 = new A ();
There a2 = new A ();
console.log(a1.name); // 1
console.log(a2.name); // 1
a1.__proto__.name = '2';
a1.name = 3;
// console.log(a1.__proto__);
console.log(a1.name); // 3
console.log(a2.name); // 2
delete a1.name;
a2.__proto__.name = '4';
console.log(a1.name); // 4
console.log(A.prototype.constructor); // A