Usage of the PostMessage API

The PostMessage API, provided by HTML5, is a cross-document communication mechanism that allows secure data transfer between different windows, iframes, or workers, bypassing the same-origin policy restrictions. Its core method, `window.postMessage`, includes data and target origin parameters. To ensure security, the `event.origin` must be validated during use. It supports the structured clone algorithm for handling complex data types. Application scenarios include cross-origin iframe communication, multi-window synchronization, Web Worker interaction, and micro-frontend architecture. Implementation requires attention to message protocol design, security validation, and performance optimization. Modern browsers widely support this API, offering advantages such as pure client-side operation, cross-origin capability, and lightweight design compared to other communication solutions. When integrating with frameworks, considerations must be given to component lifecycle and state management.

Basic concepts and application scenarios of WebRTC

WebRTC is an open framework that enables real-time browser communication, allowing audio and video transmission, data sharing, and peer-to-peer connections without plugins. Its core components include MediaStream for accessing media devices, RTCPeerConnection for establishing peer-to-peer connections, and RTCDataChannel for data transfer. Although WebRTC creates peer-to-peer connections, a signaling server is still required to coordinate communication. Typical use cases include real-time video calls, game development, and file sharing. Advanced features encompass screen sharing, recording capabilities, and network traversal techniques. Mobile adaptation requires handling platform-specific limitations on iOS and Android. Performance optimization involves bandwidth adjustment and multi-stream transmission. Security considerations include encrypted transmission and permission control. Debugging tools can monitor key metrics. Emerging applications include WebAR/VR and IoT. Enterprise-level deployment can utilize SFU architectures and media server clusters.

The CORS (Cross-Origin Resource Sharing) mechanism

Cross-Origin Resource Sharing (CORS) is a core mechanism in modern web development for handling cross-origin requests. It enables secure data interaction between different origins through HTTP header fields, overcoming the limitations of the traditional same-origin policy. The same-origin policy requires scripts to access only resources from the same origin as the current page. CORS is divided into two types: simple requests and preflight requests. Servers need to configure specific response headers, such as `Access-Control-Allow-Origin`, to permit cross-origin access. When using credentials, additional settings like `Access-Control-Allow-Credentials` are required. Common issues include preflight request failures and cross-origin cookie problems. Alternative solutions include JSONP, proxy servers, and WebSocket. Debugging can be done using browser developer tools and testing tools to inspect CORS-related request and response headers. Security considerations involve avoiding overly permissive CORS policies and properly configuring preflight request caching.

Comparison between Fetch API and XMLHttpRequest

The Fetch API and XMLHttpRequest are the two main methods for making network requests in modern browsers. The Fetch API is based on Promises, featuring concise syntax and support for async/await, while XMLHttpRequest uses callback functions and is more complex. The two differ in aspects such as request and response handling, error mechanisms, timeout control, and progress monitoring. The Fetch API is suitable for simple REST calls, whereas XMLHttpRequest offers advantages in progress monitoring and compatibility. The choice between them should be based on specific needs. Modern frameworks often encapsulate both, providing a unified interface.

The usage of Server-Sent Events (SSE)

Server-Sent Events (SSE) is an HTML5 technology that allows servers to push real-time data to clients. It is based on the HTTP protocol and uses a unidirectional communication model, making it suitable for scenarios where the server actively pushes data. Compared to WebSocket, SSE is simpler, lighter, and supports automatic reconnection. Clients receive messages through the EventSource API, while servers need to set specific response headers and follow the event stream format. SSE supports custom event types, message ID tracking, and reconnection time control, making it ideal for use cases like stock price updates and log monitoring. When using SSE, considerations include browser compatibility, security issues such as cross-origin requests and authentication, as well as performance optimizations like connection management and resource release.

Basic concepts and usage of WebSocket

WebSocket is a full-duplex communication protocol based on TCP connections, allowing servers to actively push data, making it suitable for real-time applications such as chat, gaming, and stock quotes. It establishes connections via the HTTP upgrade mechanism and features low latency, persistent connections, and cross-origin support. Modern browsers provide a WebSocket API that simplifies usage, including creating connections, sending, and receiving data. Compared to HTTP long polling, WebSocket offers superior performance, supports binary data, and subprotocols. Server-side implementations can use Node.js, with security considerations like using the wss protocol and origin validation. Practical applications include real-time chat and data monitoring. Performance optimization involves compression, batching, and heartbeat detection. Common issues include unstable connections, message order confusion, and cross-origin problems. Modern frameworks like React and Vue also support WebSocket integration.

Data synchronization and conflict resolution

Data synchronization and conflict resolution are critical challenges in modern web application development. HTML5 provides synchronization mechanisms such as polling, long polling, and WebSocket. Conflict types include write-write conflicts, sequence conflicts, and logical conflicts. Common resolution strategies include last-write-wins, operational transformation, and merge strategies. The offline-first architecture leverages Service Worker and IndexedDB, while vector clocks are used to track causality. In practical applications, shopping cart synchronization is a typical scenario. Performance optimization involves differential synchronization, batch processing, and compressed transmission. Testing requires simulating network issues, and security considerations include validation and encryption. Developers must master these skills to build robust web applications.

Cache strategy and offline resource management

HTML5 provides various caching mechanisms, including Service Worker, Cache API, etc. A reasonable caching strategy can significantly improve performance. Browser caching is divided into strong caching, negotiated caching, and application caching. Service Worker is a background script that can intercept network requests, forming the foundation of PWA. Its lifecycle includes stages such as registration, installation, and activation. The Cache API provides a mechanism for storing network requests, supporting operations like addition, deletion, modification, and query. Offline resource management employs various strategies, such as cache-first, network-first, etc. Caching requires version control, achieved by including version numbers in names. Browsers impose limits on cache storage, necessitating proper management of storage space. Advanced caching modes include runtime caching and precaching. Combining techniques like preloading and lazy loading can further optimize performance.

Basic concepts and usage of Service Worker

A Service Worker is a script that runs independently in the background of the browser, separate from the main thread of a web page. It can intercept network requests, cache resources, push messages, and more, enabling web applications to function offline and significantly improving user experience. The article unfolds step by step, from basic concepts to practical applications, covering registration, installation, request interception, caching strategies, update mechanisms, background sync, push notifications, debugging methods, performance optimization, security considerations, and real-world use cases. It provides a detailed explanation of how to leverage Service Workers to achieve advanced features like offline functionality, intelligent caching, and message推送, helping developers build more powerful web applications.

The structure and configuration of the Manifest file

The HTML5 Manifest file is a JSON-formatted metadata file used to define the configuration of web applications, particularly for Progressive Web Apps (PWAs). It allows developers to control how the app behaves in the browser, including aspects such as the name, icons, start URL, and display mode. The basic structure consists of predefined key-value pairs, such as `name` and `short_name` for app naming, and the `display` field, which determines the app's display mode with four options: `fullscreen`, `standalone`, `minimal-ui`, and `browser`. The `icons` array configures app icons of different sizes, while `theme_color` and `background_color` set the theme and background colors. The `orientation` controls the screen orientation, and `start_url` and `scope` define the launch URL and scope. Advanced features include associating native apps and defining shortcuts. The file is linked via the HTML `link` tag, and attention must be paid to browser compatibility and security considerations. In practice, the Manifest file significantly enhances the user experience and installability of PWAs.