Detailed explanation of the use of JS prototype and prototype chain
This time I will bring you a detailed explanation of the use of JS prototypes and prototype chains. What are the precautions when using JS prototypes and prototype chains? The following is a practical case, let’s take a look.
Every function we create has a prototype (prototype) attribute. This attribute is a pointer pointing to a prototype object, and the properties and methods possessed by this prototype object can be So instances are shared.
function Person(){
}
Person.prototype.name = "Nicholas";
Person.prototype.age = 29;
Person.prototype.sayName = function(){
alert(this.name);
};
var person1 = new Person();
person1.sayName(); //"Nicholas"
var person2 = new Person();
person2.sayName(); //"Nicholas"
alert(person1.sayName == person2.sayName); //true1. Understanding prototype objects
Whenever a new function is created, a prototype attribute will be created for the function according to a specific set of rules. , this attribute points to the prototype object of the function.
By default, all prototype objects automatically obtain a constructor (constructor) attribute, which contains a pointer to the function where the prototype attribute is located.
When the constructor is called to create a new instance, the instance will contain a pointer (internal property) pointing to the prototype object of the constructor. ECMA-262 version 5 refers to this pointer as [[Prototype]].
Although there is no standard way to access [[Prototype]] in scripts, Firefox, Safari, and Chrome support an attribute proto on each object; in other implementations, this attribute is available to scripts Completely invisible.
However, the really important point to make clear is that this connection exists between the instance and the prototype object of the constructor, not between the instance and the constructor.
Take the previous code that uses the Person constructor and Person.prototype to create an instance as an example. Figure 6-1 shows the relationship between each object.
Here, Person.prototype points to the prototype object, and Person.prototype.constructor points back to Person .
Both person1 and person2 contain an internal property that simply points to Person.prototype; in other words, they have no direct relationship with the constructor.
You can call person1.sayName(). This is accomplished through the process of finding object properties. (It will search on the instance first, and if it cannot be found, it will continue to search for the prototype.)
用isPrototypeOf()方法判断实例与原型对象之间的关系
alert(Person.prototype.isPrototypeOf(person1)); //true
alert(Person.prototype.isPrototypeOf(person2)); //true
用Object.getPrototypeOf() 方法返回实例的原型对象
alert(Object.getPrototypeOf(person1) == Person.prototype); //true
使用 hasOwnProperty() 方法可以检测一个属性是存在于实例中，还是存在于原型中。
alert(person1.hasOwnProperty("name")); //false 来着原型
person1.name = "Greg";
alert(person1.name); //"Greg"——来自实例
alert(person1.hasOwnProperty("name")); //true2. Simpler prototype syntax
Every addition in the previous example One attribute and method requires one type of Person.prototype. In order to reduce unnecessary typing and to better visually encapsulate the functionality of the prototype, it is more common to override the entire prototype object with an object literal that contains all properties and methods.
function Person(){
}
Person.prototype = {
name : "Nicholas",
age : 29,
job: "Software Engineer",
sayName : function () {
alert(this.name);
}
};In the above code, we set Person.prototype equal to a new object created as an object literal. The end result is the same, with one exception: the constructor property no longer points to Person .
As introduced before, every time a function is created, its prototype object will be created at the same time, and this object will also automatically obtain the constructor property.
var friend = new Person(); alert(friend instanceof Object); //true alert(friend instanceof Person); //true alert(friend.constructor == Person); //false alert(friend.constructor == Object); //true
Here, using the instanceof operator to test Object and Person still returns true, but the constructor property is equal to Object and not equal to Person.
If the value of constructor is really important, you can deliberately set it back to the appropriate value as shown below.
function Person(){
}
Person.prototype = {
constructor : Person,
name : "Nicholas",
age : 29,
job: "Software Engineer",
sayName : function () {
alert(this.name);
}
};3. Prototype of native object
All native reference types (Object, Array, String, etc.) have methods defined on the prototype of their constructor .
For example, the sort() method can be found in Array.prototype, and the substring() method can be found in String.prototype. Although it is possible to do so, it is not recommended to modify the prototype of a native object.
4. Problems with prototype objects
The biggest problem with the prototype pattern is caused by its shared nature. Modifying one of them will affect the other.
function Person(){
}
Person.prototype = {
constructor: Person,
name : "Nicholas",
age : 29,
job : "Software Engineer",
friends : ["Shelby", "Court"],
sayName : function () {
alert(this.name);
}
};
var person1 = new Person();
var person2 = new Person();
person1.friends.push("Van");
alert(person1.friends); //"Shelby,Court,Van"
alert(person2.friends); //"Shelby,Court,Van"
alert(person1.friends === person2.friends); //true5. Prototype chain
The basic idea is to use prototypes to let one reference type inherit the properties and methods of another reference type. Then, layer by layer, a chain of instances and prototypes is formed. This is the basic concept of the so-called prototype chain.
function SuperType(){
this.property = true;
}
SuperType.prototype.getSuperValue = function(){
return this.property;
};
function SubType(){
this.subproperty = false;
}
//继承了 SuperType
SubType.prototype = new SuperType();
SubType.prototype.getSubValue = function (){
return this.subproperty;
};
var instance = new SubType();
alert(instance.getSuperValue()); //trueA picture description:
I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!
Recommended reading:
Detailed explanation of Servlet3.0 and JS through Ajax interaction example
Vue implementation of tree menu step instructions
The above is the detailed content of Detailed explanation of the use of JS prototype and prototype chain. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
What software is crystaldiskmark? -How to use crystaldiskmark?
Mar 18, 2024 pm 02:58 PM
CrystalDiskMark is a small HDD benchmark tool for hard drives that quickly measures sequential and random read/write speeds. Next, let the editor introduce CrystalDiskMark to you and how to use crystaldiskmark~ 1. Introduction to CrystalDiskMark CrystalDiskMark is a widely used disk performance testing tool used to evaluate the read and write speed and performance of mechanical hard drives and solid-state drives (SSD). Random I/O performance. It is a free Windows application and provides a user-friendly interface and various test modes to evaluate different aspects of hard drive performance and is widely used in hardware reviews
How to download foobar2000? -How to use foobar2000
Mar 18, 2024 am 10:58 AM
foobar2000 is a software that can listen to music resources at any time. It brings you all kinds of music with lossless sound quality. The enhanced version of the music player allows you to get a more comprehensive and comfortable music experience. Its design concept is to play the advanced audio on the computer The device is transplanted to mobile phones to provide a more convenient and efficient music playback experience. The interface design is simple, clear and easy to use. It adopts a minimalist design style without too many decorations and cumbersome operations to get started quickly. It also supports a variety of skins and Theme, personalize settings according to your own preferences, and create an exclusive music player that supports the playback of multiple audio formats. It also supports the audio gain function to adjust the volume according to your own hearing conditions to avoid hearing damage caused by excessive volume. Next, let me help you
How to use Baidu Netdisk app
Mar 27, 2024 pm 06:46 PM
Cloud storage has become an indispensable part of our daily life and work nowadays. As one of the leading cloud storage services in China, Baidu Netdisk has won the favor of a large number of users with its powerful storage functions, efficient transmission speed and convenient operation experience. And whether you want to back up important files, share information, watch videos online, or listen to music, Baidu Cloud Disk can meet your needs. However, many users may not understand the specific use method of Baidu Netdisk app, so this tutorial will introduce in detail how to use Baidu Netdisk app. Users who are still confused can follow this article to learn more. ! How to use Baidu Cloud Network Disk: 1. Installation First, when downloading and installing Baidu Cloud software, please select the custom installation option.
How to use NetEase Mailbox Master
Mar 27, 2024 pm 05:32 PM
NetEase Mailbox, as an email address widely used by Chinese netizens, has always won the trust of users with its stable and efficient services. NetEase Mailbox Master is an email software specially created for mobile phone users. It greatly simplifies the process of sending and receiving emails and makes our email processing more convenient. So how to use NetEase Mailbox Master, and what specific functions it has. Below, the editor of this site will give you a detailed introduction, hoping to help you! First, you can search and download the NetEase Mailbox Master app in the mobile app store. Search for "NetEase Mailbox Master" in App Store or Baidu Mobile Assistant, and then follow the prompts to install it. After the download and installation is completed, we open the NetEase email account and log in. The login interface is as shown below
BTCC tutorial: How to bind and use MetaMask wallet on BTCC exchange?
Apr 26, 2024 am 09:40 AM
MetaMask (also called Little Fox Wallet in Chinese) is a free and well-received encryption wallet software. Currently, BTCC supports binding to the MetaMask wallet. After binding, you can use the MetaMask wallet to quickly log in, store value, buy coins, etc., and you can also get 20 USDT trial bonus for the first time binding. In the BTCCMetaMask wallet tutorial, we will introduce in detail how to register and use MetaMask, and how to bind and use the Little Fox wallet in BTCC. What is MetaMask wallet? With over 30 million users, MetaMask Little Fox Wallet is one of the most popular cryptocurrency wallets today. It is free to use and can be installed on the network as an extension
Detailed explanation of obtaining administrator rights in Win11
Mar 08, 2024 pm 03:06 PM
Windows operating system is one of the most popular operating systems in the world, and its new version Win11 has attracted much attention. In the Win11 system, obtaining administrator rights is an important operation. Administrator rights allow users to perform more operations and settings on the system. This article will introduce in detail how to obtain administrator permissions in Win11 system and how to effectively manage permissions. In the Win11 system, administrator rights are divided into two types: local administrator and domain administrator. A local administrator has full administrative rights to the local computer
Detailed explanation of division operation in Oracle SQL
Mar 10, 2024 am 09:51 AM
Detailed explanation of division operation in OracleSQL In OracleSQL, division operation is a common and important mathematical operation, used to calculate the result of dividing two numbers. Division is often used in database queries, so understanding the division operation and its usage in OracleSQL is one of the essential skills for database developers. This article will discuss the relevant knowledge of division operations in OracleSQL in detail and provide specific code examples for readers' reference. 1. Division operation in OracleSQL
Teach you how to use the new advanced features of iOS 17.4 'Stolen Device Protection'
Mar 10, 2024 pm 04:34 PM
Apple rolled out the iOS 17.4 update on Tuesday, bringing a slew of new features and fixes to iPhones. The update includes new emojis, and EU users will also be able to download them from other app stores. In addition, the update also strengthens the control of iPhone security and introduces more "Stolen Device Protection" setting options to provide users with more choices and protection. "iOS17.3 introduces the "Stolen Device Protection" function for the first time, adding extra security to users' sensitive information. When the user is away from home and other familiar places, this function requires the user to enter biometric information for the first time, and after one hour You must enter information again to access and change certain data, such as changing your Apple ID password or turning off stolen device protection.
