Web Front-end
JS Tutorial
Detailed explanation of deep and shallow copy examples of JavaScript objects
Detailed explanation of deep and shallow copy examples of JavaScript objects
From a hierarchical perspective, the copying of objects can be simply divided into shallow copying and deep copying. As the name suggests, shallow copying refers to copying only the properties of one layer of objects and not copying the properties of objects in the object. Deep copying of objects Properties of nested objects within the object will be copied. This article is a summary of some of my experiences in copying objects, from shallow copy to deep copy. Friends who are interested can learn together
Preface
From a hierarchical perspective, the copying of objects can be simply divided into shallow copying and deep copying. As the name suggests, shallow copying refers to copying only the properties of one layer of objects and will not copy the properties of objects in the object. Deep copying of objects will copy the objects. Properties of nested objects.
When copying an object, in addition to copying the properties of the object, you must also consider whether the constructor property of the object is retained and whether each data type (common data types in Javascript include String, Number, Boolean, Data, RegExp, Array, Function, Object) all achieve correct copying. In the project, we can decide what level of replication needs to be achieved based on the actual situation.
This article is a summary of some of my experiences in copying objects, from shallow copy to deep copy, from copying only simple attributes to copying complex attributes such as Function and RegExp, and progresses layer by layer. If there is anything inappropriate in the statement, please point it out, I would be very grateful.
Text
Shallow copy
Shallow copy will only copy each attribute of the object in sequence , these properties will not be copied recursively. Below is a simple shallow copy implementation.
//对象浅复制
function shadowCopy(obj){
if(typeof obj !== 'object') return obj;
for(var prop in obj){
if(obj.hasOwnProperty(prop)){
newObj[prop] = obj[prop];
}
}
return newObj;
}Observe carefully, it is not difficult to find the flaws of the above method:
1. The shallow copy of the array cannot be correctly implemented
2. The copy operation loses the constructor attribute of the object
Okay, we have now discovered the problem. We only need to solve it in a targeted manner, and a fairly perfect method of shallow copying objects is born!
//对象浅复制
function shadowCopy(obj){
if(typeof obj !== 'object') return ;
var newObj;
//保留对象的constructor属性
if(obj.constructor === Array){
newObj = [];
} else {
newObj = {};
newObj.constructor = obj.constructor;
}
for(var prop in obj){
if(obj.hasOwnProperty(prop)){
newObj[prop] = obj[prop];
}
}
return newObj;
}Test it in the browser:
var arr1 = [0,1,2]; console.log(arr1); console.log(shadowCopy(arr1)); var arr2 = [0,1,2,[3,4,5]], arr2Copy = shadowCopy(arr2); console.log(arr2); console.log(arr2Copy); arr2Copy[3][0] = 6; console.log(arr2[3][0]); //6
Good! The array copy and constructor can be correctly implemented and the constructor is retained. , but if you are careful, you must have discovered that arr2Copy[3] and arr2[3] of the shallowly copied object point to the same object. Changing one of them will also change the other. What we want to achieve is replication, but this is not replication!
This is one of the drawbacks of shallow copying. Let's see how deep copying solves this problem.
Deep copy
Deep copy requires layers of recursion, copying all the properties of the object, including the properties of the properties of the object....(Halo~)
If you just need to simply copy the properties of an object without considering its constructor or special data types such as functions, regulars, and data, then here is a small trick for deep copying, just two lines of code:
function deepCopy(obj){
if(typeof obj !== "object"){ return ;}
var str = JSON.stringify(obj);
return JSON.parse(str);
}In most cases, the above can meet the requirements, but sometimes, we need to take into account special data types such as functions and regular expressions, or the current environment does not support it. When using JSON, the above method does not apply. At this time, we can implement deep copy of the object through recursion, as follows:
function deepCopy(obj){
if(typeof obj !== "object"){ return ;}
var newObj;
//保留对象的constructor属性
if(obj.constructor === Array){
newObj = [];
} else {
newObj = {};
newObj.constructor = obj.constructor;
}
for(var prop in obj){
if(typeof obj[prop] === 'object'){
if(obj[prop].constructor === RegExp ||obj[prop].constructor === Date){
newObj[prop] = obj[prop];
} else {
//递归
newObj[prop] = deepCopy(obj[prop]);
}
} else {
newObj[prop] = obj[prop];
}
}
return newObj;
}First use the above example to test:
Great! The copying of multi-dimensional arrays can be correctly realized, and then see if the copying of functions and regular expressions can be realized:
function Person(name){
this.name = name;
this.age = age;
this.search = new RegExp(name);
this.say = function(){
console.log(this.name + "今年" + this.age + "岁了");
}
}
var p1 = new Person("Claiyre",20),
p2 = deepCopy(p1);
console.log(p1);
console.log(p2);
p2.age = 22;
p1.say();
p2.say();
Successfully completed! !
With a little tidying up, we can get a more general js object copy function:
function deepCopy(obj){
var newObj = obj.constructor === Array ? []:{};
newObj.constructor = obj.constructor;
if(typeof obj !== "object"){
return ;
} else if(window.JSON){
//若需要考虑特殊的数据类型，如正则，函数等，需把这个else if去掉即可
newObj = JSON.parse(JSON.stringify(obj));
} else {
for(var prop in obj){
if(obj[prop].constructor === RegExp ||obj[prop].constructor === Date){
newObj[prop] = obj[prop];
} else if(typeof obj[prop] === 'object'){
//递归
newObj[prop] = deepCopy(obj[prop]);
} else {
newObj[prop] = obj[prop];
}
}
}
return newObj;
}Conclusion
The core of object-oriented programming language is objects. Therefore, in-depth understanding of the related operations of objects and vertical comparison of similarities and differences are extremely beneficial to the learning process.
The above is the detailed content of Detailed explanation of deep and shallow copy examples of JavaScript objects. 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
How to use JS and Baidu Maps to implement map pan function
Nov 21, 2023 am 10:00 AM
How to use JS and Baidu Map to implement map pan function Baidu Map is a widely used map service platform, which is often used in web development to display geographical information, positioning and other functions. This article will introduce how to use JS and Baidu Map API to implement the map pan function, and provide specific code examples. 1. Preparation Before using Baidu Map API, you first need to apply for a developer account on Baidu Map Open Platform (http://lbsyun.baidu.com/) and create an application. Creation completed
Recommended: Excellent JS open source face detection and recognition project
Apr 03, 2024 am 11:55 AM
Face detection and recognition technology is already a relatively mature and widely used technology. Currently, the most widely used Internet application language is JS. Implementing face detection and recognition on the Web front-end has advantages and disadvantages compared to back-end face recognition. Advantages include reducing network interaction and real-time recognition, which greatly shortens user waiting time and improves user experience; disadvantages include: being limited by model size, the accuracy is also limited. How to use js to implement face detection on the web? In order to implement face recognition on the Web, you need to be familiar with related programming languages and technologies, such as JavaScript, HTML, CSS, WebRTC, etc. At the same time, you also need to master relevant computer vision and artificial intelligence technologies. It is worth noting that due to the design of the Web side
How to create a stock candlestick chart using PHP and JS
Dec 17, 2023 am 08:08 AM
How to use PHP and JS to create a stock candle chart. A stock candle chart is a common technical analysis graphic in the stock market. It helps investors understand stocks more intuitively by drawing data such as the opening price, closing price, highest price and lowest price of the stock. price fluctuations. This article will teach you how to create stock candle charts using PHP and JS, with specific code examples. 1. Preparation Before starting, we need to prepare the following environment: 1. A server running PHP 2. A browser that supports HTML5 and Canvas 3
Essential tools for stock analysis: Learn the steps to draw candle charts with PHP and JS
Dec 17, 2023 pm 06:55 PM
Essential tools for stock analysis: Learn the steps to draw candle charts in PHP and JS. Specific code examples are required. With the rapid development of the Internet and technology, stock trading has become one of the important ways for many investors. Stock analysis is an important part of investor decision-making, and candle charts are widely used in technical analysis. Learning how to draw candle charts using PHP and JS will provide investors with more intuitive information to help them make better decisions. A candlestick chart is a technical chart that displays stock prices in the form of candlesticks. It shows the stock price
How to use JS and Baidu Map to implement map click event processing function
Nov 21, 2023 am 11:11 AM
Overview of how to use JS and Baidu Maps to implement map click event processing: In web development, it is often necessary to use map functions to display geographical location and geographical information. Click event processing on the map is a commonly used and important part of the map function. This article will introduce how to use JS and Baidu Map API to implement the click event processing function of the map, and give specific code examples. Steps: Import the API file of Baidu Map. First, import the file of Baidu Map API in the HTML file. This can be achieved through the following code:
How to use JS and Baidu Maps to implement map heat map function
Nov 21, 2023 am 09:33 AM
How to use JS and Baidu Maps to implement the map heat map function Introduction: With the rapid development of the Internet and mobile devices, maps have become a common application scenario. As a visual display method, heat maps can help us understand the distribution of data more intuitively. This article will introduce how to use JS and Baidu Map API to implement the map heat map function, and provide specific code examples. Preparation work: Before starting, you need to prepare the following items: a Baidu developer account, create an application, and obtain the corresponding AP
PHP and JS Development Tips: Master the Method of Drawing Stock Candle Charts
Dec 18, 2023 pm 03:39 PM
With the rapid development of Internet finance, stock investment has become the choice of more and more people. In stock trading, candle charts are a commonly used technical analysis method. It can show the changing trend of stock prices and help investors make more accurate decisions. This article will introduce the development skills of PHP and JS, lead readers to understand how to draw stock candle charts, and provide specific code examples. 1. Understanding Stock Candle Charts Before introducing how to draw stock candle charts, we first need to understand what a candle chart is. Candlestick charts were developed by the Japanese
The relationship between js and vue
Mar 11, 2024 pm 05:21 PM
The relationship between js and vue: 1. JS as the cornerstone of Web development; 2. The rise of Vue.js as a front-end framework; 3. The complementary relationship between JS and Vue; 4. The practical application of JS and Vue.
