search
HomeWeb Front-endHTML TutorialJS异步那些事 四(HTML 5 Web Workers)_html/css_WEB-ITnose

什么是 Web Worker?

当在 HTML 页面中执行脚本时,页面的状态是不可响应的,直到脚本已完成。web worker 是运行在后台的 JavaScript,独立于其他脚本,不会影响页面的性能。您可以继续做任何愿意做的事情:点击、选取内容等等,而此时 web worker 在后台运行。

创建 web worker 文件

现在,让我们在一个外部 JavaScript 中创建我们的 web worker。在这里,我们创建了计数脚本。该脚本存储于 “demo_workers.js” 文件中:

var i=0;function timedCount(){i=i+1;postMessage(i);setTimeout("timedCount()",500);}timedCount();

以上代码中重要的部分是 postMessage() 方法 – 它用于向 HTML 页面传回一段消息。

注释:web worker 通常不用于如此简单的脚本,而是用于更耗费 CPU 资源的任务。

创建 Web Worker 对象

我们已经有了 web worker 文件,现在我们需要从 HTML 页面调用它。下面的代码检测是否存在 worker,如果不存在,- 它会创建一个新的 web worker 对象,然后运行 “demo_workers.js” 中的代码:

if(typeof(w)=="undefined")  {  w=new Worker("demo_workers.js");  }

然后我们就可以从 web worker 发生和接收消息了。向 web worker 添加一个 “onmessage” 事件监听器:

w.onmessage=function(event){document.getElementById("result").innerHTML=event.data;};

当 web worker 传递消息时,会执行事件监听器中的代码。event.data 中存有来自 event.data 的数据。

终止 Web Worker

当我们创建 web worker 对象后,它会继续监听消息(即使在外部脚本完成之后)直到其被终止为止。

如需终止 web worker,并释放浏览器/计算机资源,请使用 terminate() 方法:

w.terminate();

完整的 Web Worker 实例代码

我们已经看到了 .js 文件中的 Worker 代码。下面是 HTML 页面的代码:

<!DOCTYPE html><html><body><p>Count numbers: <output id="result"></output></p><button onclick="startWorker()">Start Worker</button><button onclick="stopWorker()">Stop Worker</button><br /><br /><script>var w;function startWorker(){if(typeof(Worker)!=="undefined"){  if(typeof(w)=="undefined")    {    w=new Worker("demo_workers.js");    }  w.onmessage = function (event) {    document.getElementById("result").innerHTML=event.data;  };}else{document.getElementById("result").innerHTML="Sorry, your browser does not support Web Workers...";}}function stopWorker(){w.terminate();}</script></body></html>

本文参考w3cschool中HTML 5 Web worker的解释

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
What is the purpose of HTML tags?What is the purpose of HTML tags?Apr 28, 2025 am 12:02 AM

HTMLtagsareessentialforstructuringwebpages,enhancingaccessibility,SEO,andperformance.1)Theyareenclosedinanglebracketsandusedinpairstocreateahierarchicalstructure.2)SemantictagslikeandimproveuserexperienceandSEO.3)Creativetagslikeenabledynamicgraphics

What are self-closing tags? Give an example.What are self-closing tags? Give an example.Apr 27, 2025 am 12:04 AM

Self-closingtagsinHTMLandXMLaretagsthatclosethemselveswithoutneedingaseparateclosingtag,simplifyingmarkupstructureandenhancingcodingefficiency.1)TheyareessentialinXMLforelementswithoutcontent,ensuringwell-formeddocuments.2)InHTML5,usageisflexiblebutr

Beyond HTML: Essential Technologies for Web DevelopmentBeyond HTML: Essential Technologies for Web DevelopmentApr 26, 2025 am 12:04 AM

To build a website with powerful functions and good user experience, HTML alone is not enough. The following technology is also required: JavaScript gives web page dynamic and interactiveness, and real-time changes are achieved by operating DOM. CSS is responsible for the style and layout of the web page to improve aesthetics and user experience. Modern frameworks and libraries such as React, Vue.js and Angular improve development efficiency and code organization structure.

What are boolean attributes in HTML? Give some examples.What are boolean attributes in HTML? Give some examples.Apr 25, 2025 am 12:01 AM

Boolean attributes are special attributes in HTML that are activated without a value. 1. The Boolean attribute controls the behavior of the element by whether it exists or not, such as disabled disable the input box. 2.Their working principle is to change element behavior according to the existence of attributes when the browser parses. 3. The basic usage is to directly add attributes, and the advanced usage can be dynamically controlled through JavaScript. 4. Common mistakes are mistakenly thinking that values ​​need to be set, and the correct writing method should be concise. 5. The best practice is to keep the code concise and use Boolean properties reasonably to optimize web page performance and user experience.

How can you validate your HTML code?How can you validate your HTML code?Apr 24, 2025 am 12:04 AM

HTML code can be cleaner with online validators, integrated tools and automated processes. 1) Use W3CMarkupValidationService to verify HTML code online. 2) Install and configure HTMLHint extension in VisualStudioCode for real-time verification. 3) Use HTMLTidy to automatically verify and clean HTML files in the construction process.

HTML vs. CSS and JavaScript: Comparing Web TechnologiesHTML vs. CSS and JavaScript: Comparing Web TechnologiesApr 23, 2025 am 12:05 AM

HTML, CSS and JavaScript are the core technologies for building modern web pages: 1. HTML defines the web page structure, 2. CSS is responsible for the appearance of the web page, 3. JavaScript provides web page dynamics and interactivity, and they work together to create a website with a good user experience.

HTML as a Markup Language: Its Function and PurposeHTML as a Markup Language: Its Function and PurposeApr 22, 2025 am 12:02 AM

The function of HTML is to define the structure and content of a web page, and its purpose is to provide a standardized way to display information. 1) HTML organizes various parts of the web page through tags and attributes, such as titles and paragraphs. 2) It supports the separation of content and performance and improves maintenance efficiency. 3) HTML is extensible, allowing custom tags to enhance SEO.

The Future of HTML, CSS, and JavaScript: Web Development TrendsThe Future of HTML, CSS, and JavaScript: Web Development TrendsApr 19, 2025 am 12:02 AM

The future trends of HTML are semantics and web components, the future trends of CSS are CSS-in-JS and CSSHoudini, and the future trends of JavaScript are WebAssembly and Serverless. 1. HTML semantics improve accessibility and SEO effects, and Web components improve development efficiency, but attention should be paid to browser compatibility. 2. CSS-in-JS enhances style management flexibility but may increase file size. CSSHoudini allows direct operation of CSS rendering. 3.WebAssembly optimizes browser application performance but has a steep learning curve, and Serverless simplifies development but requires optimization of cold start problems.

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

Video Face Swap

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Tools

SublimeText3 English version

SublimeText3 English version

Recommended: Win version, supports code prompts!

ZendStudio 13.5.1 Mac

ZendStudio 13.5.1 Mac

Powerful PHP integrated development environment

Safe Exam Browser

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.

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

EditPlus Chinese cracked version

EditPlus Chinese cracked version

Small size, syntax highlighting, does not support code prompt function