Web Front-endJS TutorialA brief discussion on onbeforeunload and onunload events in JavaScript_Basic knowledge
In a recent project, I need to cache part of the content of the page when the user leaves the page. However, I don’t need to cache it when the user refreshes. I only want it to be cached when the user leaves. time
Execute this function. According to Baidu, there are two events: onbeforeunload and onunload, but onbeforeunload will also be executed when the user refreshes. It took me a long time to do this, so I want to make a small summary here
onbeforeunload and onunload events
onbeforeunload definition and usage
The onbeforeunload event is triggered when the current page is about to be left (refreshed or closed).
This event can be used to pop up a dialog box to prompt the user whether to continue browsing the page or leave the current page.
The default prompt message of the dialog box varies according to different browsers. The standard message is similar to "Are you sure you want to leave this page?". This information cannot be deleted.
But you can customize some message prompts to be displayed in the dialog box together with the standard information.
Note: If you do not specify the onbeforeunload event on the
element, you need to add the event on the window object and create custom information using the returnValue attribute (see the following syntax example).Note: In the Firefox browser, only the default reminder information is displayed (customized information is not displayed).
How to use:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>test</title>
</head>
<body onbeforeunload="return test()">
</body>
<script type="text/javascript">
function test(){
return "你确定要离开吗";
}
</script>
</html>
or:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>test</title>
</head>
<body>
</body>
<script type="text/javascript">
window.onbeforeunload=function(){
return "你确定要离开吗";
}
</script>
</html>
When the event is triggered, a dialog box with confirmation and cancellation pops up. If you confirm, you will leave the page, and if you cancel, you will continue to stay on this page. Of course you can customize the prompt text.
So, what should I do when I only need to execute this function when I leave, but not when refreshing?
window.onbeforeunload = function() {
var n = window.event.screenX - window.screenLeft;
var b = n > document.documentElement.scrollWidth - 20;
if (!(b && window.event.clientY < 0 || window.event.altKey)) {
//window.event.returnValue = "真的要刷新页面么？";
//这里放置我想执行缓存的代码
cacheFunction();
}
}
In this way, when I leave the page, I can execute my cache code without popping up the prompt box. When I refresh, the prompt box will not pop up and it will not be executed. It is worth mentioning that at this time, ajax should be set to synchronization, that is: async in ajax should be changed to: false;
Browser compatibility
Perfect support for IE, Chrome and Safari
Firefox does not support text reminder messages
Opera does not support
Bugs encountered by IE6 and IE7 when using onbeforeunload
2. Onunload definition and usage
The onunload event occurs when the user exits the page.
Usage is similar to onbeforeunload
window.onunload = function(){
return "你确定要离开吗"
}
Browser compatibility
In IE6, IE7, IE8, it will be executed after refreshing the page, closing the browser, and after page jump;
IE9 will execute the page refresh, but the page jump and closing the browser will not execute;
firefox (including firefox3.6) can be executed after closing the tag, after page jump, and after refreshing the page, but it cannot be executed after closing the browser;
Safari will execute after refreshing the page and page jump, but it will not execute when closing the browser;
Opera and Chrome will not be executed under any circumstances.
Summary
Onunload and onbeforeunload are called when refreshing or closing. They can be specified through window.onunload in the <script> script or specified in <body>. The difference is that onbeforeunload is executed before onunload, and it can also prevent the execution of onunload. <br /> Onbeforeunload is also called when the page is refreshed or closed. Onbeforeunload is called when going to the server to read a new page, but it has not yet started reading; while onunload has read the new page that needs to be loaded from the server and is about to replace it. Called when the current page is deleted. Onunload cannot prevent the page from being updated and closed. And Onbeforeunload can do it. </script>
Onload is only executed when the page loads
When the page is closed, onbeforeunload is executed first, and finally onunload
When the page is refreshed, onbeforeunload is executed first, then onunload, and finally onload.
Replace String Characters in JavaScriptMar 11, 2025 am 12:07 AMDetailed explanation of JavaScript string replacement method and FAQ This article will explore two ways to replace string characters in JavaScript: internal JavaScript code and internal HTML for web pages. Replace string inside JavaScript code The most direct way is to use the replace() method: str = str.replace("find","replace"); This method replaces only the first match. To replace all matches, use a regular expression and add the global flag g: str = str.replace(/fi
Custom Google Search API Setup TutorialMar 04, 2025 am 01:06 AMThis tutorial shows you how to integrate a custom Google Search API into your blog or website, offering a more refined search experience than standard WordPress theme search functions. It's surprisingly easy! You'll be able to restrict searches to y
8 Stunning jQuery Page Layout PluginsMar 06, 2025 am 12:48 AMLeverage jQuery for Effortless Web Page Layouts: 8 Essential Plugins jQuery simplifies web page layout significantly. This article highlights eight powerful jQuery plugins that streamline the process, particularly useful for manual website creation
Build Your Own AJAX Web ApplicationsMar 09, 2025 am 12:11 AMSo here you are, ready to learn all about this thing called AJAX. But, what exactly is it? The term AJAX refers to a loose grouping of technologies that are used to create dynamic, interactive web content. The term AJAX, originally coined by Jesse J
What is 'this' in JavaScript?Mar 04, 2025 am 01:15 AMCore points This in JavaScript usually refers to an object that "owns" the method, but it depends on how the function is called. When there is no current object, this refers to the global object. In a web browser, it is represented by window. When calling a function, this maintains the global object; but when calling an object constructor or any of its methods, this refers to an instance of the object. You can change the context of this using methods such as call(), apply(), and bind(). These methods call the function using the given this value and parameters. JavaScript is an excellent programming language. A few years ago, this sentence was
10 Mobile Cheat Sheets for Mobile DevelopmentMar 05, 2025 am 12:43 AMThis post compiles helpful cheat sheets, reference guides, quick recipes, and code snippets for Android, Blackberry, and iPhone app development. No developer should be without them! Touch Gesture Reference Guide (PDF) A valuable resource for desig
Improve Your jQuery Knowledge with the Source ViewerMar 05, 2025 am 12:54 AMjQuery is a great JavaScript framework. However, as with any library, sometimes it’s necessary to get under the hood to discover what’s going on. Perhaps it’s because you’re tracing a bug or are just curious about how jQuery achieves a particular UI
How do I create and publish my own JavaScript libraries?Mar 18, 2025 pm 03:12 PMArticle discusses creating, publishing, and maintaining JavaScript libraries, focusing on planning, development, testing, documentation, and promotion strategies.
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
SublimeText3 English version
Recommended: Win version, supports code prompts!
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.
Zend Studio 13.0.1
Powerful PHP integrated development environment
DVWA
Damn Vulnerable Web App (DVWA) is a PHP/MySQL web application that is very vulnerable. Its main goals are to be an aid for security professionals to test their skills and tools in a legal environment, to help web developers better understand the process of securing web applications, and to help teachers/students teach/learn in a classroom environment Web application security. The goal of DVWA is to practice some of the most common web vulnerabilities through a simple and straightforward interface, with varying degrees of difficulty. Please note that this software
mPDF
mPDF is a PHP library that can generate PDF files from UTF-8 encoded HTML. The original author, Ian Back, wrote mPDF to output PDF files "on the fly" from his website and handle different languages. It is slower than original scripts like HTML2FPDF and produces larger files when using Unicode fonts, but supports CSS styles etc. and has a lot of enhancements. Supports almost all languages, including RTL (Arabic and Hebrew) and CJK (Chinese, Japanese and Korean). Supports nested block-level elements (such as P, DIV),
