Further understanding of js closures
The content shared with you in this article is about further understanding of js closures. The content is very good. Friends in need can refer to it.
The concept of closure has been confusing to me since I started learning JS a few months ago
I understood it before, but then I didn’t use it for a long time Just forgot
Closure: In layman’s terms, what most people accept is that a function has the right to use local variables in another function
I see a lot of differences
Use the simplest code to express
<span style="font-size: 14px;">function out(){<br/><br/>var age=21;<br/><br/>function inner(){<br/> <br/> console.log(age);<br/><br/>}<br/><br/>return inner;<br/><br/>}<br/><br/>var fn=out();<br/> fn(); //22</span>Very consistent with the concept
I think closure is reflecting the scope
The inner function is defined inside the out function
So console(age);
will use the variable search mechanism. First, search within the scope of your own (inner) function. If not found, go to Find
in the out function scope and then output. If not found in out, it will look for
in a larger scope. Until the scope of the window, the lower-level scope can be accessed upwards, but the upper-level scope cannot be accessed downwards
Scope refers to
{ }
And JS does not have block-level scope
for(var i=0;i<5;i){
console.log(i);// 1 2 3 4 5
}
cosole.log(i );//5
i will not be destroyed just because the for loop is out.
This should be noted
Okay, I talked about a little bit about scope. Now back to closures
The core of closures is return. Just look at the code and you will know.
My understanding is that return returns the function body of inner and the scope that inner can access!
So inner can be accessed anywhere age
Example:
<span style="font-size: 14px;">function test(){<br/> var age=23;<br/> var fn=out();<br/> fn(); //21<br/> <br/> }<br/> <br/> test();//21</span>It gets 21 instead of 22 because the function body and scope are returned together Then the nearest scope is the out function scope.
Even if age is defined in the test function, it cannot be overwritten because the existing scopes are different
It returns the scope, so it accesses all the variables in that scope and has nothing to do with the scope where your function is now.
Closure is actually a This phenomenon is that everyone who plays DNF is painting pictures and selling materials to make money. This phenomenon is called moving bricks
To sum up: it has to do with the scope of the function you define, and the role of the function you execute. Domain-independent
Contrary to this, this has nothing to do with definition time and is related to execution time. Compare memory
So if you don’t understand it well Closure
Then you can understand it like me
What is returned is the function itself and the scope that the function can access
Give one commonly used one
Closure Tab bar switching
<span style="font-size: 14px;"><!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="Generator" content="EditPlus®">
<meta name="Author" content="">
<meta name="Keywords" content="">
<meta name="Description" content="">
<title>Document</title>
<style type="text/css">
*{margin:0;padding:0<span style="font-size: 12px; color: rgb(0, 0, 0);">;}
.box{
width:140px;
height:18px;
position:relative;
padding:6px 20px;
margin:50px auto;
background:#ff6666;
}
.box ul{
list</span>-<span style="font-size: 12px; color: rgb(0, 0, 0);">style:none;
}
.box li{
width:18px;
height:18px;
background:#ff3300;
line</span>-<span style="font-size: 12px; color: rgb(0, 0, 0);">height:18px;
text</span>-<span style="font-size: 12px; color: rgb(0, 0, 0);">align:center; </span><span style="font-size: 12px; color: rgb(0, 0, 255);">float</span><span style="font-size: 12px; color: rgb(0, 0, 0);">:left;
margin</span>-<span style="font-size: 12px; color: rgb(0, 0, 0);">right:5px;
cursor:pointer;
}
.current{
background:#ffccff</span>!<span style="font-size: 12px; color: rgb(0, 0, 0);">important;
} </span></style>
</head>
<body>
<p class="box">
<ul>
<li>1</li>
<li>2</li>
<li>3</li>
<li>4</li>
<li>5</li>
<li>6</li>
</ul>
</p>
<script type="text/javascript"> <br/><span style="font-size: 12px; color: rgb(0, 0, 255);">function</span><span style="font-size: 12px; color: rgb(0, 0, 0);"> $(name){ <br/> <br/></span><span style="font-size: 12px; color: rgb(0, 0, 255);">return</span><span style="font-size: 12px; color: rgb(0, 0, 0);"> document.querySelectorAll(name);
} <br/> <br/></span><span style="font-size: 12px; color: rgb(0, 0, 255);">var</span> list=$(".box ul li"<span style="font-size: 12px; color: rgb(0, 0, 0);">); <br/><br/></span><span style="font-size: 12px; color: rgb(0, 0, 255);">var</span> len=<span style="font-size: 12px; color: rgb(0, 0, 0);">list.length; <br/> </span><span style="font-size: 12px; color: rgb(0, 0, 255);">for</span>(<span style="font-size: 12px; color: rgb(0, 0, 255);">var</span> i=0;i<len;i++<span style="font-size: 12px; color: rgb(0, 0, 0);">){
list[i].onmouseover</span>=(<span style="font-size: 12px; color: rgb(0, 0, 255);">function</span><span style="font-size: 12px; color: rgb(0, 0, 0);">(n){
</span><span style="font-size: 12px; color: rgb(0, 0, 255);">return</span> <span style="font-size: 12px; color: rgb(0, 0, 255);">function</span><span style="font-size: 12px; color: rgb(0, 0, 0);">(){ <br/><br/></span><span style="font-size: 12px; color: rgb(0, 0, 255);">for</span>(<span style="font-size: 12px; color: rgb(0, 0, 255);">var</span> j=0;j<len;j++<span style="font-size: 12px; color: rgb(0, 0, 0);">){
list[j].className</span>=""<span style="font-size: 12px; color: rgb(0, 0, 0);">;
}
list[n].className</span>="current"<span style="font-size: 12px; color: rgb(0, 0, 0);">;
}
})(i);
}<br/><br/><br/><br/></span></script>
</body>
</html></span>
Whenever the for loop executes list[i].onmouseover, the function will be executed immediately and the current variable i is passed in
Return a function. This forms a closure. Return the function and the scope that the function can access.
Whenever onmouseover is triggered, the returned function will be executed.
Then execute the for loop in the generation function to clear all li's className
This sentence is the most important when executing list[n]. The n here is the i ## passed in when defining onmouseover
# Because the function is executed immediately when it is defined and i is passed to the anonymous function. This i is within the scope of the anonymous function
Each onmouseover saves its own i
, so when triggered Onmouseover allows li to access the i
that was previously saved in the scope, thus realizing the need to change the background color of someone
Related recommendations:Understanding of actual parameters, formal parameters and closures of js functions
The above is the detailed content of Further understanding of js closures. 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 should I do if I encounter garbled code printing for front-end thermal paper receipts?
Apr 04, 2025 pm 02:42 PM
Frequently Asked Questions and Solutions for Front-end Thermal Paper Ticket Printing In Front-end Development, Ticket Printing is a common requirement. However, many developers are implementing...
Demystifying JavaScript: What It Does and Why It Matters
Apr 09, 2025 am 12:07 AM
JavaScript is the cornerstone of modern web development, and its main functions include event-driven programming, dynamic content generation and asynchronous programming. 1) Event-driven programming allows web pages to change dynamically according to user operations. 2) Dynamic content generation allows page content to be adjusted according to conditions. 3) Asynchronous programming ensures that the user interface is not blocked. JavaScript is widely used in web interaction, single-page application and server-side development, greatly improving the flexibility of user experience and cross-platform development.
Who gets paid more Python or JavaScript?
Apr 04, 2025 am 12:09 AM
There is no absolute salary for Python and JavaScript developers, depending on skills and industry needs. 1. Python may be paid more in data science and machine learning. 2. JavaScript has great demand in front-end and full-stack development, and its salary is also considerable. 3. Influencing factors include experience, geographical location, company size and specific skills.
How to merge array elements with the same ID into one object using JavaScript?
Apr 04, 2025 pm 05:09 PM
How to merge array elements with the same ID into one object in JavaScript? When processing data, we often encounter the need to have the same ID...
Is JavaScript hard to learn?
Apr 03, 2025 am 12:20 AM
Learning JavaScript is not difficult, but it is challenging. 1) Understand basic concepts such as variables, data types, functions, etc. 2) Master asynchronous programming and implement it through event loops. 3) Use DOM operations and Promise to handle asynchronous requests. 4) Avoid common mistakes and use debugging techniques. 5) Optimize performance and follow best practices.
How to achieve parallax scrolling and element animation effects, like Shiseido's official website?
or:
How can we achieve the animation effect accompanied by page scrolling like Shiseido's official website?
Apr 04, 2025 pm 05:36 PM
Discussion on the realization of parallax scrolling and element animation effects in this article will explore how to achieve similar to Shiseido official website (https://www.shiseido.co.jp/sb/wonderland/)...
The difference in console.log output result: Why are the two calls different?
Apr 04, 2025 pm 05:12 PM
In-depth discussion of the root causes of the difference in console.log output. This article will analyze the differences in the output results of console.log function in a piece of code and explain the reasons behind it. �...
How to implement panel drag and drop adjustment function similar to VSCode in front-end development?
Apr 04, 2025 pm 02:06 PM
Explore the implementation of panel drag and drop adjustment function similar to VSCode in the front-end. In front-end development, how to implement VSCode similar to VSCode...
