HTML5中有哪些不同类型的存储？

Local Storage 持久存储字符串数据，适用于跨会话保存用户设置；2. Session Storage 仅在会话期间保留数据，适合临时存储如表单草稿；3. Web Storage 是前两者的统称，仅支持字符串键值对；4. IndexedDB 可持久化大量结构化数据，支持事务和索引，适合复杂离线应用；5. Cache API 用于缓存网络请求响应，实现 PWA 离线功能；6. Web SQL 已弃用，不应在新项目中使用；选择存储方式应根据数据类型、持久性需求和容量要求决定。

HTML5 introduced several client-side storage options that allow web applications to store data directly in the user's browser. These storage types differ in capacity, persistence, and use cases. Here are the main types:

1. Local Storage

• Purpose: Stores data with no expiration time.
• Persistence: Data remains even after the browser is closed or the page is reloaded.
• Capacity: Typically around 5–10 MB per domain.
• Usage: Ideal for saving user preferences, settings, or cached data that should persist across sessions.
• Example:

  localStorage.setItem('username', 'john_doe');
  let name = localStorage.getItem('username');

2. Session Storage

• Purpose: Stores data for one session only.
• Persistence: Data is cleared when the browser tab or window is closed.
• Capacity: Similar to local storage (~5–10 MB).
• Usage: Useful for temporary data like form inputs during a checkout process.
• Example:

  sessionStorage.setItem('tempData', 'draft');
  let data = sessionStorage.getItem('tempData');

3. Web Storage (Local & Session Together)

• This is a collective term for both localStorage and sessionStorage.
• Both use simple key-value string pairs.
• Limitation: Only stores strings; objects must be serialized (e.g., using JSON.stringify).

4. IndexedDB

• Purpose: A low-level API for storing large amounts of structured data, including files and blobs.
• Persistence: Data persists unless explicitly deleted.
• Capacity: Much larger — can be hundreds of MB or more, depending on the browser and device.
• Usage: Suitable for complex web apps (e.g., offline note apps, games with saved progress).
• Features:
  • Supports transactions
  • Allows indexing for fast searches
  • Asynchronous API (doesn’t block the main thread)
• More complex to use than Web Storage.

5. Cache API (Part of Service Workers)

• Purpose: Designed for storing HTTP responses (e.g., HTML, CSS, JS, images).
• Use Case: Enables offline functionality in Progressive Web Apps (PWAs).
• Controlled via JavaScript and usually used with service workers.
• Example:

  caches.open('v1').then(cache => {
    cache.add('/styles.css');
  });

6. Web SQL (Deprecated)

• Note: Was a database system based on SQL, but is deprecated and not supported in most modern browsers.
• Avoid using it for new projects.

Summary of Key Differences:

Each storage option serves a different need. For simple data, use localStorage or sessionStorage. For rich, offline-capable apps, go with IndexedDB and Cache API.

Basically, choose the right tool based on how much data you need, whether it should survive a page reload, and what kind of data it is.

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