W3school.com.cn Site Title
w3school 在线教程
W3school.com.cn Meta Description
全球最大的中文 Web 技术教程。
W3school.com.cn Test Results
W3school.com.cn Mobile Performance: 55/100
Quick overview:
Opportunities
These suggestions can help your page load faster. They don't directly affect the Performance score.
Avoid multiple page redirects. Potential savings of 1,740 ms
Redirects introduce additional delays before the page can be loaded. Learn more.
Serve images in next-gen formats. Potential savings of 143 KiB
Image formats like JPEG 2000, JPEG XR, and WebP often provide better compression than PNG or JPEG, which means faster downloads and less data consumption. Learn more.
Reduce initial server response time. Root document took 1,070 ms
Keep the server response time for the main document short because all other requests depend on it. Learn more.
Eliminate render-blocking resources. Potential savings of 150 ms
Resources are blocking the first paint of your page. Consider delivering critical JS/CSS inline and deferring all non-critical JS/styles. Learn more.
Diagnostics
More information about the performance of your application. These numbers don't directly affect the Performance score.
Reduce the impact of third-party code
Third-party code blocked the main thread for 1,170 ms
Third-party code can significantly impact load performance. Limit the number of redundant third-party providers and try to load third-party code after your page has primarily finished loading. Learn more.
Minimize main-thread work
2.5 s
Consider reducing the time spent parsing, compiling and executing JS. You may find delivering smaller JS payloads helps with this. Learn more
Keep request counts low and transfer sizes small
22 requests • 303 KiB
To set budgets for the quantity and size of page resources, add a budget.json file. Learn more.
Avoid chaining critical requests
1 chain found
The Critical Request Chains below show you what resources are loaded with a high priority. Consider reducing the length of chains, reducing the download size of resources, or deferring the download of unnecessary resources to improve page load. Learn more.
Avoid long main-thread tasks
7 long tasks found
Lists the longest tasks on the main thread, useful for identifying worst contributors to input delay. Learn more
Largest Contentful Paint element
1 element found
This is the largest contentful element painted within the viewport. Learn More
W3school.com.cn Mobile SEO: 73/100
Quick overview:
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`
Add a `<meta name="viewport">` tag to optimize your app for mobile screens. Learn more. No `<meta name="viewport">` tag found
Tap targets are not sized appropriately
Interactive elements like buttons and links should be large enough (48x48px), and have enough space around them, to be easy enough to tap without overlapping onto other elements. Learn more. Tap targets are too small because there's no viewport meta tag optimized for mobile screens
Document doesn't use legible font sizes
Font sizes less than 12px are too small to be legible and require mobile visitors to “pinch to zoom” in order to read. Strive to have >60% of page text ≥12px. Learn more. Text is illegible because there's no viewport meta tag optimized for mobile screens.
W3school.com.cn Mobile Best Practices: 85/100
Quick overview:
Trust and Safety
Does not use HTTPS
2 insecure requests found
All sites should be protected with HTTPS, even ones that don't handle sensitive data. This includes avoiding mixed content, where some resources are loaded over HTTP despite the initial request being servedover HTTPS. HTTPS prevents intruders from tampering with or passively listening in on the communications between your app and your users, and is a prerequisite for HTTP/2 and many new web platform APIs. Learn more.
Links to cross-origin destinations are unsafe
Add `rel="noopener"` or `rel="noreferrer"` to any external links to improve performance and prevent security vulnerabilities. Learn more.
W3school.com.cn Mobile Progressive Web App: 39/100
Quick overview:
PWA Optimized
Manifest doesn't have a maskable icon
A maskable icon ensures that the image fills the entire shape without being letterboxed when installing the app on a device. Learn more. No manifest was fetched
Is not configured for a custom splash screen
A themed splash screen ensures a high-quality experience when users launch your app from their homescreens. Learn more. Failures: No manifest was fetched.
Content is not sized correctly for the viewport
If the width of your app's content doesn't match the width of the viewport, your app might not be optimized for mobile screens. Learn more. The viewport size of 1239px does not match the window size of 360px.
Does not set a theme color for the address bar.
The browser address bar can be themed to match your site. Learn more. Failures: No manifest was fetched,
No `<meta name="theme-color">` tag found.
Does not have a `<meta name="viewport">` tag with `width` or `initial-scale`
Add a `<meta name="viewport">` tag to optimize your app for mobile screens. Learn more. No `<meta name="viewport">` tag found
Fast and reliable
`start_url` does not respond with a 200 when offline
A service worker enables your web app to be reliable in unpredictable network conditions. Learn more. No usable web app manifest found on page.
Current page does not respond with a 200 when offline
If you're building a Progressive Web App, consider using a service worker so that your app can work offline. Learn more.
Installable
Does not use HTTPS
2 insecure requests found
All sites should be protected with HTTPS, even ones that don't handle sensitive data. This includes avoiding mixed content, where some resources are loaded over HTTP despite the initial request being servedover HTTPS. HTTPS prevents intruders from tampering with or passively listening in on the communications between your app and your users, and is a prerequisite for HTTP/2 and many new web platform APIs. Learn more.
Web app manifest does not meet the installability requirements
Browsers can proactively prompt users to add your app to their homescreen, which can lead to higher engagement. Learn more. Failures: No manifest was fetched.
Does not register a service worker that controls page and `start_url`
The service worker is the technology that enables your app to use many Progressive Web App features, such as offline, add to homescreen, and push notifications. Learn more.
W3school.com.cn Mobile Accessibility: 100/100
Quick overview:
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