What are js deep copy and shallow copy and how to implement them
Today I will tell you about the deep copy and shallow copy of JS. What is the difference between them and what are their functions? Let me give you an example below.
var m = { a: 10, b: 20 }var n = m;n.a = 15;//What is the value of m.a at this time?
m.a will output 15, Because this is a shallow copy, n and m point to the same heap, object copy is just a reference of the copied object.
Deep copy
Deep copy is different from the above shallow copy, which is to completely copy an object instead of copying the reference of the object. For example, in the previous example, we write like this:
var m = { a: 10, b: 20 }var n = {a:m.a,b:m.b};n.a = 15;
This time, we output m.a again and find that m.a The value is still 10 and has not changed. Although all the values of the m object and the n object are the same, they are not the same in the heap. This is a deep copy.
Deep copy and shallow copy
The schematic diagram of deep copy and shallow copy is roughly as follows:
Shallow copy only copies points to a certain object pointer without copying the object itself, the old and new objects still share the same memory. However, a deep copy will create an identical object. The new object does not share memory with the original object, and modifications to the new object will not change the original object.
How to implement shallow copy
1. It can be implemented through simple assignment
Similar to the above example, of course, we can also encapsulate a simple function, as follows:
function simpleClone(initalObj) {
var obj = {};
for ( var i in initalObj) {
obj[i] = initalObj[i];
}
return obj;
}
var obj = {
a: "hello",
b:{
a: "world",
b: 21
},
c:["Bob", "Tom", "Jenny"],
d:function() {
alert("hello world");
}
}
var cloneObj = simpleClone(obj);
console.log(cloneObj.b);
console.log(cloneObj.c);
console.log(cloneObj.d);
cloneObj.b.a = "changed";
cloneObj.c = [1, 2, 3];
cloneObj.d = function() { alert("changed"); };
console.log(obj.b);
console.log(obj.c);
console.log(obj.d);2, Object.assign() implements the
Object.assign() method to copy any number of source object’s own enumerable properties to the target object , and then returns the target object. However, Object.assign() performs a shallow copy, copying references to the object's properties rather than the object itself.
var obj = { a: {a: "hello", b: 21} };var initalObj = Object.assign({}, obj); initalObj.a.a = "changed";console.log( obj.a.a); // "changed"
Note: When the object has only one layer, it is a deep copy, for example, as follows:
var obj1 = { a: 10, b: 20, c: 30 };var obj2 = Object.assign({}, obj1);obj2.b = 100;console.log(obj1);// { a: 10, b: 20, c: 30 } <-- 沒被改到console.log(obj2);// { a: 10, b: 100, c: 30 }How to implement deep copy
1. Method 1 is still manual copying
Same as the above example, manual copying can achieve deep copy.
2. If the object has only one layer, you can use the above: Object.assign() function
3. Convert to JSON and then back again
var obj1 = { body: { a: 10 } };var obj2 = JSON.parse(JSON.stringify(obj1));obj2.body.a = 20;console.log(obj1);// { body: { a: 10 } } <-- 沒被改到console.log(obj2);// { body: { a: 20 } }console.log(obj1 === obj2);// falseconsole.log(obj1.body === obj2.body);// falseUse JSON.stringify to Convert the object into a string, and then use JSON.parse to convert the string into a new object.
You can encapsulate the following functions
var cloneObj = function(obj){
var str, newobj = obj.constructor === Array ? [] : {};
if(typeof obj !== 'object'){
return;
} else if(window.JSON){
str = JSON.stringify(obj), //系列化对象
newobj = JSON.parse(str); //还原
} else {
for(var i in obj){
newobj[i] = typeof obj[i] === 'object' ?
cloneObj(obj[i]) : obj[i];
}
}
return newobj;};4. Recursive copy
function deepClone(initalObj, finalObj) {
var obj = finalObj || {};
for (var i in initalObj) {
var prop = initalObj[i]; // 避免相互引用对象导致死循环，如initalObj.a = initalObj的情况
if(prop === obj) {
continue;
}
if (typeof prop === 'object') {
obj[i] = (prop.constructor === Array) ? [] : {};
arguments.callee(prop, obj[i]);
} else {
obj[i] = prop;
}
}
return obj;}var str = {};var obj = { a: {a: "hello", b: 21} };deepClone(obj, str);console.log(str.a);5. Use the Object.create() method
Use var newObj = Object directly. create(oldObj) can achieve the effect of deep copy.
function deepClone(initalObj, finalObj) {
var obj = finalObj || {};
for (var i in initalObj) {
var prop = initalObj[i]; // 避免相互引用对象导致死循环，如initalObj.a = initalObj的情况
if(prop === obj) {
continue;
}
if (typeof prop === 'object') {
obj[i] = (prop.constructor === Array) ? [] : Object.create(prop);
} else {
obj[i] = prop;
}
}
return obj;}6, jquery
jquery provides a $.extend that can be used for Deep Copy.
var $ = require('jquery');var obj1 = {
a: 1,
b: { f: { g: 1 } },
c: [1, 2, 3]};var obj2 = $.extend(true, {}, obj1);console.log(obj1.b.f === obj2.b.f);// false7, lodash
Another very popular function library, lodash, also provides _.cloneDeep for Deep Copy.
var _ = require('lodash');var obj1 = {
a: 1,
b: { f: { g: 1 } },
c: [1, 2, 3]};var obj2 = _.cloneDeep(obj1);console.log(obj1.b.f === obj2.b.f);// falseThis performance is not bad and it is very simple to use.
I believe you have mastered the methods after reading these cases. For more exciting information, please pay attention to other related articles on the php Chinese website!
Related reading:
How to deal with the incomplete display of the last line of text in HTML
How to use css3 to create icon effects
The above is the detailed content of What are js deep copy and shallow copy and how to implement them. 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
1655
14
1414
52
1307
25
1253
29
1228
24
How to implement dual WeChat login on Huawei mobile phones?
Mar 24, 2024 am 11:27 AM
How to implement dual WeChat login on Huawei mobile phones? With the rise of social media, WeChat has become one of the indispensable communication tools in people's daily lives. However, many people may encounter a problem: logging into multiple WeChat accounts at the same time on the same mobile phone. For Huawei mobile phone users, it is not difficult to achieve dual WeChat login. This article will introduce how to achieve dual WeChat login on Huawei mobile phones. First of all, the EMUI system that comes with Huawei mobile phones provides a very convenient function - dual application opening. Through the application dual opening function, users can simultaneously
PHP Programming Guide: Methods to Implement Fibonacci Sequence
Mar 20, 2024 pm 04:54 PM
The programming language PHP is a powerful tool for web development, capable of supporting a variety of different programming logics and algorithms. Among them, implementing the Fibonacci sequence is a common and classic programming problem. In this article, we will introduce how to use the PHP programming language to implement the Fibonacci sequence, and attach specific code examples. The Fibonacci sequence is a mathematical sequence defined as follows: the first and second elements of the sequence are 1, and starting from the third element, the value of each element is equal to the sum of the previous two elements. The first few elements of the sequence
How to implement the WeChat clone function on Huawei mobile phones
Mar 24, 2024 pm 06:03 PM
How to implement the WeChat clone function on Huawei mobile phones With the popularity of social software and people's increasing emphasis on privacy and security, the WeChat clone function has gradually become the focus of people's attention. The WeChat clone function can help users log in to multiple WeChat accounts on the same mobile phone at the same time, making it easier to manage and use. It is not difficult to implement the WeChat clone function on Huawei mobile phones. You only need to follow the following steps. Step 1: Make sure that the mobile phone system version and WeChat version meet the requirements. First, make sure that your Huawei mobile phone system version has been updated to the latest version, as well as the WeChat App.
Master how Golang enables game development possibilities
Mar 16, 2024 pm 12:57 PM
In today's software development field, Golang (Go language), as an efficient, concise and highly concurrency programming language, is increasingly favored by developers. Its rich standard library and efficient concurrency features make it a high-profile choice in the field of game development. This article will explore how to use Golang for game development and demonstrate its powerful possibilities through specific code examples. 1. Golang’s advantages in game development. As a statically typed language, Golang is used in building large-scale game systems.
PHP Game Requirements Implementation Guide
Mar 11, 2024 am 08:45 AM
PHP Game Requirements Implementation Guide With the popularity and development of the Internet, the web game market is becoming more and more popular. Many developers hope to use the PHP language to develop their own web games, and implementing game requirements is a key step. This article will introduce how to use PHP language to implement common game requirements and provide specific code examples. 1. Create game characters In web games, game characters are a very important element. We need to define the attributes of the game character, such as name, level, experience value, etc., and provide methods to operate these
How to implement exact division operation in Golang
Feb 20, 2024 pm 10:51 PM
Implementing exact division operations in Golang is a common need, especially in scenarios involving financial calculations or other scenarios that require high-precision calculations. Golang's built-in division operator "/" is calculated for floating point numbers, and sometimes there is a problem of precision loss. In order to solve this problem, we can use third-party libraries or custom functions to implement exact division operations. A common approach is to use the Rat type from the math/big package, which provides a representation of fractions and can be used to implement exact division operations.
Using PHP to implement SaaS: a comprehensive analysis
Mar 07, 2024 pm 10:18 PM
I'm really sorry that I can't provide real-time programming guidance, but I can provide you with a code example to give you a better understanding of how to use PHP to implement SaaS. The following is an article within 1,500 words, titled "Using PHP to implement SaaS: A comprehensive analysis." In today's information age, SaaS (Software as a Service) has become the mainstream way for enterprises and individuals to use software. It provides a more flexible and convenient way to access software. With SaaS, users don’t need to be on-premises
Detailed explanation of using Golang to implement data export function
Feb 28, 2024 pm 01:42 PM
Title: Detailed explanation of data export function using Golang. With the improvement of informatization, many enterprises and organizations need to export data stored in databases into different formats for data analysis, report generation and other purposes. This article will introduce how to use the Golang programming language to implement the data export function, including detailed steps to connect to the database, query data, and export data to files, and provide specific code examples. To connect to the database first, we need to use the database driver provided in Golang, such as da
