W3school.com.cn w3school 在线教程
全球最大的中文 Web 技术教程。
w3school.com.cn Desktop Performance
80/100
These metrics represent real-world Chrome users experience viewing w3school.com.cn web page. Reports are focused on loading performance and other critical factors that most affect user experience. Follow our guide to track, optimize, and improve the quality of your web pages.
User Loading Experience
Largest Contentful Paint
First Contentful Paint
First Input Delay
Cumulative Layout Shift
Metrics
Speed Index27/100 3.0 s
Speed Index shows how quickly the contents of a page are visibly populated. Learn more.
First Contentful Paint64/100 1.4 s
First Contentful Paint marks the time at which the first text or image is painted. Learn more.
Largest Contentful Paint85/100 1.4 s
Largest Contentful Paint marks the time at which the largest text or image is painted. Learn More
Time to Interactive99/100 1.4 s
Time to interactive is the amount of time it takes for the page to become fully interactive. Learn more.
Total Blocking Time100/100 0 ms
Sum of all time periods between FCP and Time to Interactive, when task length exceeded 50ms, expressed in milliseconds. Learn more.
Cumulative Layout Shift100/100 0
Cumulative Layout Shift measures the movement of visible elements within the viewport. Learn more.
Should Fix (7)
Opportunities
These suggestions can help your page load faster. They don't directly affect the Performance score.
Avoid multiple page redirects
Potential savings of 530 ms
530 ms
Reduce initial server response time
Root document took 850 ms
251 ms
Serve images in next-gen formats
Potential savings of 80 KiB
160 ms
Diagnostics
More information about the performance of your application. These numbers don't directly affect the Performance score.
Avoid chaining critical requests
1 chain found
Keep request counts low and transfer sizes small
22 requests • 198 KiB
Largest Contentful Paint element
1 element found
Avoid long main-thread tasks
1 long task found
Passed Audits (21)
Properly size images
Eliminate render-blocking resources
Potential savings of 0 ms
Use video formats for animated content
All text remains visible during webfont loads
Preload key requests
Avoids `document.write()`
Defer offscreen images
JavaScript execution time
0.0 s
Minify CSS
Preconnect to required origins
Minimizes main-thread work
0.5 s
Minimize third-party usage
Third-party code blocked the main thread for 240 ms
Uses efficient cache policy on static assets
1 resource found
Minify JavaScript
Efficiently encode images
Enable text compression
Remove unused CSS
Uses passive listeners to improve scrolling performance
Avoids enormous network payloads
Total size was 198 KiB
Avoids an excessive DOM size
330 elements
Remove unused JavaScript
w3school.com.cn Desktop SEO
89/100
These checks ensure that your page is optimized for search engine results ranking. There are additional factors Lighthouse does not check that may affect your search ranking. Learn more. Run these additional validators on your site to check additional SEO best practices.
Should Fix (1)
Mobile Friendly
Make sure your pages are mobile friendly so users don’t have to pinch or zoom in order to read the content pages. Learn more.
Does not have a `<meta name="viewport">` tag with `width` or `initial-scale`
Passed Audits (8)
Links have descriptive text
Links are crawlable
Document has a `<title>` element
Document has a valid `hreflang`
Document avoids plugins
Document has a meta description
Page has successful HTTP status code
Page isn’t blocked from indexing
w3school.com.cn Desktop Best Practices
85/100
These checks highlight opportunities to improve the overall code health of w3school.com.cn page. Current recommendations will help to make your page fast and secure, to create a good user experience and to avoid deprecated technologies.
Should Fix (2)
Trust and Safety
Does not use HTTPS
2 insecure requests found
Links to cross-origin destinations are unsafe
Passed Audits (12)
Avoids Application Cache
Detected JavaScript libraries
Displays images with correct aspect ratio
Avoids front-end JavaScript libraries with known security vulnerabilities
Serves images with appropriate resolution
No browser errors logged to the console
Avoids deprecated APIs
Avoids requesting the notification permission on page load
Page has the HTML doctype
Allows users to paste into password fields
Avoids requesting the geolocation permission on page load
Properly defines charset
w3school.com.cn Desktop Progressive Web App
0/100
These checks validate the aspects of a Progressive Web App. Learn more. These checks are required by the baseline PWA Checklist but are not automatically checked by Lighthouse. They do not affect your score but it's important that you verify them manually.
Should Fix (11)
PWA Optimized
Manifest doesn't have a maskable icon
Does not set a theme color for the address bar.
Does not have a `<meta name="viewport">` tag with `width` or `initial-scale`
Is not configured for a custom splash screen
Contains some content when JavaScript is not available
Redirects HTTP traffic to HTTPS
Fast and reliable
`start_url` does not respond with a 200 when offline
Current page does not respond with a 200 when offline
Installable
Does not use HTTPS
2 insecure requests found
Does not register a service worker that controls page and `start_url`
Web app manifest does not meet the installability requirements
Passed Audits (2)
Provides a valid `apple-touch-icon`
Page load is fast enough on mobile networks
w3school.com.cn Desktop Accessibility
100/100
These checks highlight opportunities to improve the accessibility of your web app. Only a subset of accessibility issues can be automatically detected so manual testing is also encouraged. These items address areas which an automated testing tool cannot cover. Learn more in our guide on conducting an accessibility review.
Passed Audits (12)
Links have a discernible name
Background and foreground colors have a sufficient contrast ratio
Lists contain only `<li>` elements and script supporting elements (`<script>` and `<template>`).
`<html>` element has a valid value for its `[lang]` attribute
Document has a `<title>` element
Form elements have associated labels
`[id]` attributes on active, focusable elements are unique
`<html>` element has a `[lang]` attribute
List items (`<li>`) are contained within `<ul>` or `<ol>` parent elements
`[aria-hidden="true"]` is not present on the document `<body>`
Heading elements appear in a sequentially-descending order
The page contains a heading, skip link, or landmark region
Desktop Speed
88/100
These checks analyze the performance of w3school.com.cn on desktop devices and return PageSpeed score and information on how to improve the load time. What makes a good Progressive Web App?
Should Fix (4)
Leverage browser caching
Optimize images
Eliminate render-blocking JavaScript and CSS in above-the-fold content
Minify CSS
Passed Audits (6)
Avoid landing page redirects
Enable compression
Reduce server response time
Minify HTML
Minify JavaScript
Prioritize visible content
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