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

When using HTML5SSE, the methods to deal with reconnection and errors include: 1. Understand the default reconnection mechanism. EventSource retrys 3 seconds after the connection is interrupted by default. You can customize the interval through the retry field; 2. Listen to the error event to deal with connection failure or parsing errors, distinguish error types and execute corresponding logic, such as network problems relying on automatic reconnection, server errors manually delay reconnection, and authentication failure refresh token; 3. Actively control the reconnection logic, such as manually closing and rebuilding the connection, setting the maximum number of retry times, combining navigator.onLine to judge network status to optimize the retry strategy. These measures can improve application stability and user experience.

To call GeolocationAPI, you need to use the navigator.geolocation.getCurrentPosition() method, and pay attention to permissions, environment and configuration. First check whether the browser supports API, and then call getCurrentPosition to obtain location information; the user needs to authorize access to the location; the deployment environment should be HTTPS; the accuracy or timeout can be improved through configuration items; the mobile behavior may be limited by device settings; the error type can be identified through error.code and given corresponding prompts in the failed callback to improve user experience and functional stability.

The core reason why browsers restrict the automatic playback of HTML5 videos is to improve the user experience and prevent unauthorized sound playback and resource consumption. The main strategies include: 1. When there is no user interaction, audio automatic playback is prohibited by default; 2. Allow mute automatic playback; 3. Audio videos must be played after the user clicks. The methods to achieve compatibility include: setting muted properties, mute first and then play in JS, and waiting for user interaction before playing. Browsers such as Chrome and Safari perform slightly differently on this strategy, but the overall trend is consistent. Developers can optimize the experience by first mute playback and provide an unmute button, monitoring user clicks, and handling playback exceptions. These restrictions are particularly strict on mobile devices, with the aim of avoiding unexpected traffic consumption and multiple videos

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.

Doctype is a statement that tells the browser which HTML standard to use to parse the page. Modern web pages only need to be written at the beginning of the HTML file. Its function is to ensure that the browser renders the page in standard mode rather than weird mode, and must be located on the first line, with no spaces or comments in front of it; there is only one correct way to write it, and it is not recommended to use old versions or other variants; other such as charset, viewport, etc. should be placed in part.