Let’s not talk about concepts. Let’s talk about examples

const a = new Array(a); a.__proto__ = ? a.constructor =?Copy the code

Array.prototype and Array

  • a.__proto__ 和 Array.prototypeIt’s a thing,prototypeIs unique to constructors;
  • ArrayIs a function,The blue dotted lineisArrayThe thing to do isPrototype chainA part of;

The __proto__ constructor assigns its prototype to the instance’s __proto__.

If it’s more abstract, let’s see

function A (name) {
  this.name = name;
};

var a = new A('smart a'); ??

console.log(a.__proto__ === A.prototype); ??
console.log(A.__proto__ === Function.prototype); ??
console.log(Function.__proto__ === Function.prototype); ??
console.log(Function.prototype.__proto__ === Object.prototype); ??

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What is the output?

console.log(a.__proto__ === A.prototype); // true
console.log(A.__proto__ === Function.prototype); // true
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The first two are easy to understand

Since instance (a) is constructed by function A, it is true that instance (a) is constructed by function A. By whom? Function is the second easy explanation

What about the third one? Self equal to self?

console.log(Function.__proto__ === Function.prototype); // true
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Function is a special kind of Function, and like Array, it is generated by constructors, and constructors are functions;

So go on and on, where does it end?

console.log(Function.prototype.__proto__ === Object.prototype); ??
console.log(Object.prototype.__proto__ === null); ?? 
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Function. Protytype. __proto__ is equivalent to Object. Prototype; Function.

console.log(Object.prototype.__proto__ === null); // true
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So finally, object.prototype. __proto__, according to the rule, its constructor is prototype, but here is the end of the prototype link null, here is not why, this is the specification;

The process of always looking up is called the prototype chain

conclusion

A variable’s __proto__ always refers to the prototype of its constructor, and its endpoint is null; And this process has been looking for through prototype, that is, the prototype chain;