


What is a pattern
I was preparing for the final exam a while ago. It was so tiring and tiring, and I really didn’t have time to update the article. Today I will talk to you about the design patterns in JavaScript.
First of all, what we need to know is: a pattern is a reusable solution, while an anti-pattern is a poor solution to a certain problem.
Common examples of js anti-patterns
1. Pass strings to setTimeout and setInterval instead of functions, which triggers the internal use of eval().
2. Define a large number of variables in the global context to pollute the global namespace
3. Modify the prototype of the Object class
4. Use js in inline form. The js code embedded in the HTML file cannot be included in external unit testing tools.
5. Abusing document.write. If document.write is executed after the page is loaded, it will rewrite the page we are on. If you can use document.creatElement instead, try not to use document.write.
Categories of design patterns
Creative Design Pattern
Creative design patterns focus on handling object creation mechanisms to create objects in a way that is appropriate for a given situation. Properties that fall into this category include:
Constructor, Factory, Abstract, Prototype, Singleton and Builder
Structural Design Pattern
Structural patterns are about object composition and can often be used to find simple ways to establish relationships between different objects.
Patterns that fall into this category include:
Decorator, Facade appearance, Flyweight, Adapter adapter and Proxy agent
Behavioral Design Patterns
Behavioral patterns focus on improving or simplifying communication between different objects in the system.
Behavior patterns include:
Iterator, Mediator, Observer and Visitor
Factory mode
In order to solve the problem of multiple similar object declarations, we can use a method called factory pattern. This method is to solve the problem of a large number of duplications when instantiating objects.
Classification of Factory Pattern
Factory mode is divided into simple factory, abstract factory and smart factory. Factory mode does not require the use of a constructor explicitly.
Simple Factory Pattern: Use a class (usually a singleton) to generate instances.
Complex factory pattern: Use subclasses to determine which specific class instance a member variable should be.
Benefits of Factory Model
The main benefit is that you can eliminate the coupling between objects by using engineering methods instead of the new keyword. Prevent code duplication by centralizing all instantiation code in one location.
Disadvantages of factory model
For most classes, it is best to use the new keyword and constructor, which can make the code simpler and easier to read. Rather than having to look at the factory method to find out.
The factory pattern solves the problem of repeated instantiation, but there is another problem, that is, the problem of identification, because it is impossible to figure out which object they are instances of.
alert(typeof test1); //Object
alert(test1 instanceof Object); //true
When to use factory pattern?
Factory mode is mainly used in the following scenarios:
1. When objects or components involve high complexity
2. When you need to easily generate different instances of an object according to different environments
3. When dealing with many small objects or components that share the same properties
Constructor pattern
Constructor (constructor method) can be used in ECMAScript to create specific objects. This mode can just solve the problem that the above factory mode cannot identify object instances.
Using the constructor method not only solves the problem of repeated instantiation, but also solves the problem of object recognition. The difference between this mode and the factory mode is:
1. The constructor method does not create an object explicitly (new Object());
2. Directly assign properties and methods to this object;
3. There is no renturn statement.
There are some specifications for constructor methods:
1. The function name and the instantiation constructor name are the same and capitalized (PS: It is not mandatory, but writing this way helps distinguish the constructor from the ordinary function);
2. To create an object through a constructor, you must use the new operator.
Since objects can be created through constructors, where does this object come from, and where is new Object() executed? The execution process is as follows:
1. When a constructor is used and new constructor() is used, new Object() is executed in the background;
2. Give the scope of the constructor to the new object (that is, the object created by new Object()), and this in the function body represents the object created by new Object().
3. Execute the code within the constructor;
4. Return the new object (return directly in the background).
Constructor with prototype
There is an attribute called prototype in js. After calling the js constructor to create an object, the new object will have all the properties of the constructor prototype. In this way, multiple Car objects can be created and have access to the same prototype.
Now a single instance of run() can be shared among all Car objects.

去掉重复并排序的方法:1、使用“Array.from(new Set(arr))”或者“[…new Set(arr)]”语句,去掉数组中的重复元素,返回去重后的新数组;2、利用sort()对去重数组进行排序,语法“去重数组.sort()”。

本篇文章给大家带来了关于JavaScript的相关知识,其中主要介绍了关于Symbol类型、隐藏属性及全局注册表的相关问题,包括了Symbol类型的描述、Symbol不会隐式转字符串等问题,下面一起来看一下,希望对大家有帮助。

怎么制作文字轮播与图片轮播?大家第一想到的是不是利用js,其实利用纯CSS也能实现文字轮播与图片轮播,下面来看看实现方法,希望对大家有所帮助!

本篇文章给大家带来了关于JavaScript的相关知识,其中主要介绍了关于对象的构造函数和new操作符,构造函数是所有对象的成员方法中,最早被调用的那个,下面一起来看一下吧,希望对大家有帮助。

本篇文章给大家带来了关于JavaScript的相关知识,其中主要介绍了关于面向对象的相关问题,包括了属性描述符、数据描述符、存取描述符等等内容,下面一起来看一下,希望对大家有帮助。

方法:1、利用“点击元素对象.unbind("click");”方法,该方法可以移除被选元素的事件处理程序;2、利用“点击元素对象.off("click");”方法,该方法可以移除通过on()方法添加的事件处理程序。

本篇文章给大家带来了关于JavaScript的相关知识,其中主要介绍了关于BOM操作的相关问题,包括了window对象的常见事件、JavaScript执行机制等等相关内容,下面一起来看一下,希望对大家有帮助。

foreach不是es6的方法。foreach是es3中一个遍历数组的方法,可以调用数组的每个元素,并将元素传给回调函数进行处理,语法“array.forEach(function(当前元素,索引,数组){...})”;该方法不处理空数组。


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

AI Hentai Generator
Generate AI Hentai for free.

Hot Article

Hot Tools

Safe Exam Browser
Safe Exam Browser is a secure browser environment for taking online exams securely. This software turns any computer into a secure workstation. It controls access to any utility and prevents students from using unauthorized resources.

ZendStudio 13.5.1 Mac
Powerful PHP integrated development environment

SublimeText3 English version
Recommended: Win version, supports code prompts!

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools
