search
HomeWeb Front-endJS TutorialDetailed explanation of JavaScript class array objects and arguments instances

Array-like object

The so-called array-like object:
has a length attribute and several index attributes Object
For example:
var array = ['name', 'age', 'sex'];
  
var arrayLike = {
    0: 'name',
    1: 'age',
    2: 'sex',
    length: 3
}

Even so, why is it called an array-like object?
Let us look at these two objects from three aspects: reading and writing, obtaining length, and traversing.

Read and write

console.log(array[0]); // name
console.log(arrayLike[0]); // name
  
array[0] = 'new name';
arrayLike[0] = 'new name';

Length

console.log(array.length); // 3
console.log(arrayLike.length); // 3

Traversal

for(var i = 0, len = array.length; i < len; i++) {
   ……
}
for(var i = 0, len = arrayLike.length; i < len; i++) {
    ……
}
Isn’t it similar?
Can that type of array object use array methods? For example:
arrayLike.push(&#39;4&#39;);

However, the above code will report an error: arrayLike.push is not a function
So it is still an array class after all... …

Call the array method

What if the array-like method wants to use the array method willfully?
Since it cannot be called directly, we can use Function.call to call indirectly:
var arrayLike = {0: &#39;name&#39;, 1: &#39;age&#39;, 2: &#39;sex&#39;, length: 3 }
  
Array.prototype.join.call(arrayLike, &#39;&&#39;); // name&age&sex
  
Array.prototype.slice.call(arrayLike, 0); // ["name", "age", "sex"] 
// slice可以做到类数组转数组
  
Array.prototype.map.call(arrayLike, function(item){
    return item.toUpperCase();
}); 
// ["NAME", "AGE", "SEX"]

Array-like to object

In the above example, one method of converting an array to an array has been mentioned, and three more methods will be added:
var arrayLike = {0: &#39;name&#39;, 1: &#39;age&#39;, 2: &#39;sex&#39;, length: 3 }
// 1. slice
Array.prototype.slice.call(arrayLike); // ["name", "age", "sex"] 
// 2. splice
Array.prototype.splice.call(arrayLike, 0); // ["name", "age", "sex"] 
// 3. ES6 Array.from
Array.from(arrayLike); // ["name", "age", "sex"] 
// 4. apply
Array.prototype.concat.apply([], arrayLike)

So why do we talk about array-like objects? And what are the applications of class arrays?
When it comes to array-like objects, the Arguments object is an array-like object. In client-side JavaScript, some DOM methods (document.getElementsByTagName(), etc.) also return array-like objects.

Arguments object

Next, we will focus on the Arguments object.
The Arguments object is only defined in the function body, including the parameters and other properties of the function. In a function body, arguments refers to the Arguments object of the function.
For example:
function foo(name, age, sex) {
    console.log(arguments);
}
  
foo(&#39;name&#39;, &#39;age&#39;, &#39;sex&#39;)

The print result is as follows:
Detailed explanation of JavaScript class array objects and arguments instances
We can see that in addition to the index attribute and length attribute of the array, there is also a callee attribute. Next, we will introduce them one by one.

length attribute

The length attribute of the Arguments object indicates the length of the actual parameter, for example:
function foo(b, c, d){
    console.log("实参的长度为:" + arguments.length)
}
  
console.log("形参的长度为:" + foo.length)
  
foo(1)
  
// 形参的长度为:3
// 实参的长度为:1
callee attribute

Arguments The callee attribute of the object through which the function itself can be called.
Let’s talk about a solution to a classic closure interview question using callee:
var data = [];
  
for (var i = 0; i < 3; i++) {
    (data<i> = function () {
       console.log(arguments.callee.i) 
    }).i = i;
}
  
data[0]();
data[1]();
data[2]();
  
// 0
// 1
// 2</i>


Next, let’s talk about several points to note about the arguments object:


Binding of arguments and corresponding parameters

function foo(name, age, sex, hobbit) {
  
    console.log(name, arguments[0]); // name name
  
    // 改变形参
    name = &#39;new name&#39;;
  
    console.log(name, arguments[0]); // new name new name
  
    // 改变arguments
    arguments[1] = &#39;new age&#39;;
  
    console.log(age, arguments[1]); // new age new age
  
    // 测试未传入的是否会绑定
    console.log(sex); // undefined
  
    sex = &#39;new sex&#39;;
  
    console.log(sex, arguments[2]); // new sex undefined
  
    arguments[3] = &#39;new hobbit&#39;;
  
    console.log(hobbit, arguments[3]); // undefined new hobbit
  
}
  
foo(&#39;name&#39;, &#39;age&#39;)
The values ​​of the parameters passed in, the actual parameters and arguments will be shared. When no parameters are passed in, the values ​​of the actual parameters and arguments will not be shared.
Except for this In addition, the above is in non-strict mode. If it is in strict mode, the actual parameters and arguments will not be shared.

Passing parameters

Passing parameters from one function to another
// 使用 apply 将 foo 的参数传递给 bar
function foo() {
    bar.apply(this, arguments);
}
function bar(a, b, c) {
   console.log(a, b, c);
}
  
foo(1, 2, 3)
Powerful ES6

Using ES6’s... operator, we can easily convert to an array .
function func(...arguments) {
    console.log(arguments); // [1, 2, 3]
}
  
func(1, 2, 3);
Application

There are actually many applications for arguments, which will be discussed in the next series , that is, in the JavaScript topic series, we will see arguments in jQuery's extend implementation, function currying, recursion and other scenarios. This article will not go into details.
If you want to summarize these scenarios, the ones that can be thought of for the time being include:
  1. Parameters of variable length

  2. Function currying

  3. Recursive call

  4. Function overloading ...

The above is the detailed content of Detailed explanation of JavaScript class array objects and arguments instances. For more information, please follow other related articles on the PHP Chinese website!

Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
JavaScript and the Web: Core Functionality and Use CasesJavaScript and the Web: Core Functionality and Use CasesApr 18, 2025 am 12:19 AM

The main uses of JavaScript in web development include client interaction, form verification and asynchronous communication. 1) Dynamic content update and user interaction through DOM operations; 2) Client verification is carried out before the user submits data to improve the user experience; 3) Refreshless communication with the server is achieved through AJAX technology.

Understanding the JavaScript Engine: Implementation DetailsUnderstanding the JavaScript Engine: Implementation DetailsApr 17, 2025 am 12:05 AM

Understanding how JavaScript engine works internally is important to developers because it helps write more efficient code and understand performance bottlenecks and optimization strategies. 1) The engine's workflow includes three stages: parsing, compiling and execution; 2) During the execution process, the engine will perform dynamic optimization, such as inline cache and hidden classes; 3) Best practices include avoiding global variables, optimizing loops, using const and lets, and avoiding excessive use of closures.

Python vs. JavaScript: The Learning Curve and Ease of UsePython vs. JavaScript: The Learning Curve and Ease of UseApr 16, 2025 am 12:12 AM

Python is more suitable for beginners, with a smooth learning curve and concise syntax; JavaScript is suitable for front-end development, with a steep learning curve and flexible syntax. 1. Python syntax is intuitive and suitable for data science and back-end development. 2. JavaScript is flexible and widely used in front-end and server-side programming.

Python vs. JavaScript: Community, Libraries, and ResourcesPython vs. JavaScript: Community, Libraries, and ResourcesApr 15, 2025 am 12:16 AM

Python and JavaScript have their own advantages and disadvantages in terms of community, libraries and resources. 1) The Python community is friendly and suitable for beginners, but the front-end development resources are not as rich as JavaScript. 2) Python is powerful in data science and machine learning libraries, while JavaScript is better in front-end development libraries and frameworks. 3) Both have rich learning resources, but Python is suitable for starting with official documents, while JavaScript is better with MDNWebDocs. The choice should be based on project needs and personal interests.

From C/C   to JavaScript: How It All WorksFrom C/C to JavaScript: How It All WorksApr 14, 2025 am 12:05 AM

The shift from C/C to JavaScript requires adapting to dynamic typing, garbage collection and asynchronous programming. 1) C/C is a statically typed language that requires manual memory management, while JavaScript is dynamically typed and garbage collection is automatically processed. 2) C/C needs to be compiled into machine code, while JavaScript is an interpreted language. 3) JavaScript introduces concepts such as closures, prototype chains and Promise, which enhances flexibility and asynchronous programming capabilities.

JavaScript Engines: Comparing ImplementationsJavaScript Engines: Comparing ImplementationsApr 13, 2025 am 12:05 AM

Different JavaScript engines have different effects when parsing and executing JavaScript code, because the implementation principles and optimization strategies of each engine differ. 1. Lexical analysis: convert source code into lexical unit. 2. Grammar analysis: Generate an abstract syntax tree. 3. Optimization and compilation: Generate machine code through the JIT compiler. 4. Execute: Run the machine code. V8 engine optimizes through instant compilation and hidden class, SpiderMonkey uses a type inference system, resulting in different performance performance on the same code.

Beyond the Browser: JavaScript in the Real WorldBeyond the Browser: JavaScript in the Real WorldApr 12, 2025 am 12:06 AM

JavaScript's applications in the real world include server-side programming, mobile application development and Internet of Things control: 1. Server-side programming is realized through Node.js, suitable for high concurrent request processing. 2. Mobile application development is carried out through ReactNative and supports cross-platform deployment. 3. Used for IoT device control through Johnny-Five library, suitable for hardware interaction.

Building a Multi-Tenant SaaS Application with Next.js (Backend Integration)Building a Multi-Tenant SaaS Application with Next.js (Backend Integration)Apr 11, 2025 am 08:23 AM

I built a functional multi-tenant SaaS application (an EdTech app) with your everyday tech tool and you can do the same. First, what’s a multi-tenant SaaS application? Multi-tenant SaaS applications let you serve multiple customers from a sing

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
1 months agoBy尊渡假赌尊渡假赌尊渡假赌
R.E.P.O. Best Graphic Settings
1 months agoBy尊渡假赌尊渡假赌尊渡假赌
Will R.E.P.O. Have Crossplay?
1 months agoBy尊渡假赌尊渡假赌尊渡假赌

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

ZendStudio 13.5.1 Mac

ZendStudio 13.5.1 Mac

Powerful PHP integrated development environment

VSCode Windows 64-bit Download

VSCode Windows 64-bit Download

A free and powerful IDE editor launched by Microsoft

MantisBT

MantisBT

Mantis is an easy-to-deploy web-based defect tracking tool designed to aid in product defect tracking. It requires PHP, MySQL and a web server. Check out our demo and hosting services.

SecLists

SecLists

SecLists is the ultimate security tester's companion. It is a collection of various types of lists that are frequently used during security assessments, all in one place. SecLists helps make security testing more efficient and productive by conveniently providing all the lists a security tester might need. List types include usernames, passwords, URLs, fuzzing payloads, sensitive data patterns, web shells, and more. The tester can simply pull this repository onto a new test machine and he will have access to every type of list he needs.