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1. What is a constructor?

If a function is designed to create an object through the new keyword, it is a constructor.

As follows:

Function Father (name,age) {this.name = name;this.age = age;} function Father (name,age) {this.name = name;this.age = age;}

The constructor has the following characteristics:

(1) uppercase initials

(2) the constructor should be called using new

(3) after the constructor is called, an object is returned

(4) the return value of the constructor

If the returned value is a number, string, Boolean, ignore it directly, it is considered invisible.

If the returned value is an object, the returned object is used

(5) this in the constructor

When you use this in the constructor, it refers to the newly created object

2. How to create an object through the constructor?

With new, this process is also called instantiation, as follows:

Const let = new Father ('jhony',34); 3. What happens to the process of new an object?

Create a new object in memory {} bind the _ proto_ of the new object (chorme has been changed to [[Prototype]]) to the prototype of the constructor to bind the this to the new object fn.apply (obj,this) add properties to the new object if the constructor returns a non-empty object, return the new object you just created

The [[prototype]] attribute is hidden, but most current new browser implementations are represented using _ _ proto__. We can explicitly access the prototype property of the constructor.

4. What is the prototype?

Father.prototype is a prototype, it is an object, we also call it a prototype object.

Prototypes can share methods, and the this in the prototype points to the instance.

For example, Father.protoype.getAge can share a method without opening up a separate space.

5. The relationship between prototype, constructor and instance?

The implicit prototype of Object.prototype, that is, Object.prototype._proto_ ultimately points to null

Several formulas:

Object.__proto__ = = Function.prototype;Function.prototype.__proto__ = = Object.prototype;Object.prototype.__proto__ = = null;6, what is the prototype chain?

The object can look for a method based on the _ _ proto__ property until it finds or finds the top level. The _ _ proto__ that this process depends on is called the prototype chain (poof-- your own saliva translation).

7. Class?

Class is a grammatical sugar, just another way to write a constructor.

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