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This article introduces the relevant knowledge of "how to understand the JavaScript prototype chain". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

1. Relationship between archetypes

Each function in JavaScript has a prototype property, which in turn returns a prototype, which in turn has a constructor property that points to the constructor associated with it. The object instantiated by the constructor will have a _ _ proto__ attribute that points to the same memory as the constructor's prototype.

It is worth noting that the _ _ proto__ attribute has been removed from the standard, using Object.getPrototypeOf (object) and Object.setPrototypeOf (object, prototype) instead.

Now to test the relationship between the Object constructor and the prototype, the sample code is as follows:

/ / first, if Object is a constructor, you will have the prototype property var result = Object.prototypeconsole.log (result) / / get a prototype object / * * constructor property of the prototype object-> return the associated constructor * Object.getPrototypeOf (result) returns the prototype * / var result2 = result.constructorconsole.log (result2) / / [Function: Object] var result3 = Object.getPrototypeOf (result) console.log (result3) / / null pointing to the constructor.

The illustration is as follows:

When we get the prototype of Object.prototype through Object.getPrototypeOf (Object.prototype), the value returned is null, which means that we can stop looking when we find Object.prototype.

two。 Prototype chain

To make it easier for us to understand what the prototype chain is, first take a look at the following code:

Function Person (name) {this.name = name} var PP = Person.prototypevar PPC = PP.constructor// verify whether it is the same as the constructor console.log (PPC = Person) / / true// instantiate Personvar person = new Person ('one bowl week') / / get the prototype of the Person instantiated object var pP = Object.getPrototypeOf (person) / / verify whether the prototype of the Person instantiated object points to prototypeconsole.log (pP = = PP) / / true of the constructor

Virtually all constructors inherit from Object by default, as shown in the following code test:

/ / get the prototype of Person.prototype var PPP = Object.getPrototypeOf (PP) var OP = Object.prototype// to determine whether the two are equal console.log (PPP = = OP) / / true

The above code is not very clear, I drew a picture to understand:

The red line in the image above is the prototype chain, and the prototype chain is the direction of the relationship in the prototype. Until the final result is null, that is, Object.prototype, the prototype chain ends, that is, * * Object.prototype** is the end of the prototype chain.

We can set up the prototype chain of specific content through the Object.setPrototypeOf (obj, prototype) method, but it is not recommended to do so if it is not necessary, because it is very performance-consuming.

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