2017年3月广西计算机等级考试查分什么时候开始？

The way to add drag and drop functionality to a web page is to use HTML5's DragandDrop API, which is natively supported without additional libraries. The specific steps are as follows: 1. Set the element draggable="true" to enable drag; 2. Listen to dragstart, dragover, drop and dragend events; 3. Set data in dragstart, block default behavior in dragover, and handle logic in drop. In addition, element movement can be achieved through appendChild and file upload can be achieved through e.dataTransfer.files. Note: preventDefault must be called

The reason why ARIA and HTML5 semantic tags are needed is that although HTML5 semantic elements have accessibility meanings, ARIA can supplement semantics and enhance auxiliary technology recognition capabilities. For example, when legacy browsers lack support, components without native tags (such as modal boxes), and state updates need to be dynamically updated, ARIA provides finer granular control. HTML5 elements such as nav, main, aside correspond to ARIArole by default, and do not need to be added manually unless the default behavior needs to be overridden. The situations where ARIA should be added include: 1. Supplement the missing status information, such as using aria-expanded to represent the button expansion/collapse status; 2. Add semantic roles to non-semantic tags, such as using div role to implement tabs and match them

The security risks of HTML5 applications need to be paid attention to in front-end development, mainly including XSS attacks, interface security and third-party library risks. 1. Prevent XSS: Escape user input, use textContent, CSP header, input verification, avoid eval() and direct execution of JSON; 2. Protect interface: Use CSRFToken, SameSiteCookie policies, request frequency limits, and sensitive information to encrypt transmission; 3. Secure use of third-party libraries: periodic audit dependencies, use stable versions, reduce external resources, enable SRI verification, ensure that security lines have been built from the early stage of development.

HTML5, CSS and JavaScript should be efficiently combined with semantic tags, reasonable loading order and decoupling design. 1. Use HTML5 semantic tags, such as improving structural clarity and maintainability, which is conducive to SEO and barrier-free access; 2. CSS should be placed in, use external files and split by module to avoid inline styles and delayed loading problems; 3. JavaScript is recommended to be introduced in front, and use defer or async to load asynchronously to avoid blocking rendering; 4. Reduce strong dependence between the three, drive behavior through data-* attributes and class name control status, and improve collaboration efficiency through unified naming specifications. These methods can effectively optimize page performance and collaborate with teams.

Using HTML5 semantic tags can improve web structure clarity, accessibility and SEO effects. 1. Semantic tags such as,,,, and make it easier for the machine to understand the page content; 2. Each tag has a clear purpose: used in the top area, wrap navigation links, include core content, display independent articles, group relevant content, place sidebars, and display bottom information; 3. Avoid abuse when using it, ensure that only one per page, avoid excessive nesting, reasonable use and in blocks. Mastering these key points can make the web page structure more standardized and practical.

Common reasons why HTML5 videos don't play in Chrome include format compatibility, autoplay policy, path or MIME type errors, and browser extension interference. 1. Videos should be given priority to using MP4 (H.264) format, or provide multiple tags to adapt to different browsers; 2. Automatic playback requires adding muted attributes or triggering .play() with JavaScript after user interaction; 3. Check whether the file path is correct and ensure that the server is configured with the correct MIME type. Local testing is recommended to use a development server; 4. Ad blocking plug-in or privacy mode may prevent loading, so you can try to disable the plug-in, replace the traceless window or update the browser version to solve the problem.

HTML5Canvas is suitable for web graphics and animations, and uses JavaScript to operate context drawing; ① First add canvas tags to HTML and get 2D context; ② Use fillRect, arc and other methods to draw graphics; ③ Animation is achieved by clearing the canvas, redrawing, and requestAnimationFrame loops; ④ Complex functions require manual processing of event detection, image drawing and object encapsulation.

Embed web videos using HTML5 tags, supports multi-format compatibility, custom controls and responsive design. 1. Basic usage: add tags and set src and controls attributes to realize playback functions; 2. Support multi-formats: introduce different formats such as MP4, WebM, Ogg, etc. through tags to improve browser compatibility; 3. Custom appearance and behavior: hide default controls and implement style adjustment and interactive logic through CSS and JavaScript; 4. Pay attention to details: Set muted and autoplay to achieve automatic playback, use preload to control loading strategies, combine width and max-width to achieve responsive layout, and use add subtitles to enhance accessibility.