React JS DOM 與 React Native 元件樹：全面的技術比較

介紹

React JS 和 React Native 雖然共享核心原則，但在渲染和管理 UI 元素的方法上存在顯著差異。本文對 React JS 中使用的文件物件模型 (DOM) 和 React Native 使用的元件樹結構進行了深入的技術比較，包括 React Native 的新架構。

架構概覽

React JS 和 DOM

React JS 在 Web 瀏覽器中運行，操作文檔物件模型 (DOM) 來渲染和更新使用者介面。

主要特徵：

1. 虛擬 DOM：React JS 使用虛擬 DOM 作為抽象層。
2. 協調：在虛擬 DOM 和實際 DOM 之間協調變更。
3. HTML 元素：UI 元件最終呈現為標準 HTML 元素。

React Native 和元件樹

React Native 專為行動平台設計，不與 DOM 互動。相反，它管理特定於行動作業系統（iOS 或 Android）的本機元件樹。

主要特徵：

1. 原生元件：UI 元素對應到特定於平台的原生元件。
2. 橋接器：JavaScript 核心透過橋接器與本機模組進行通訊。
3. 影子樹：用C語言維護元件的影子樹，用於佈局計算。

React Native 的新架構

React Native 正在過渡到新的架構，該架構顯著改變了它處理渲染和本機交互的方式：

1. Fabric：一種新的渲染系統，可提高 UI 回應能力並允許更多並發操作。
2. TurboModules：增強的本機模組系統，提供型別安全介面和延遲載入功能。

渲染流程

反應JS

1. JSX 被轉換為 React.createElement() 呼叫。
2. 虛擬 DOM 根據狀態或 prop 變更進行更新。
3. 協調演算法將虛擬 DOM 與實際 DOM 進行比較。
4. 必要的更新會大量並套用到真實的 DOM。

<p>// React JS Component<br>
function WebButton({ onPress, title }) {<br>
  return (<br>
    <button onClick={onPress} className="web-button"><br>
      {title}<br>
    </button><br>
  );<br>
}</p>

反應本機

傳統建築：

1. JSX 被轉換為 React.createElement() 呼叫（類似於 React JS）。
2. React Native 建立原生元件的實例，而不是 DOM 節點。
3. 影子樹已更新以進行佈局計算。
4. 原生 UI 元件透過特定於平台的 API 進行更新。

新架構（結構）：

1. JSX 仍然轉換為 React.createElement() 呼叫。
2. 渲染現在用 C 完成，允許更多同步操作。
3. 陰影樹和佈局計算與原生渲染更加緊密地結合。
4. 可以更有效地應用更新，可能在單一框架中。

<p>// React Native Component (works with both architectures)<br>
import { TouchableOpacity, Text } from 'react-native';</p>

<p>function NativeButton({ onPress, title }) {<br>
  return (<br>
    <TouchableOpacity onPress={onPress}><br>
      <Text>{title}</Text><br>
    </TouchableOpacity><br>
  );<br>
}</p>

性能影響

反應JS

• 優點：
  1. 虛擬 DOM 可最大限度地減少實際 DOM 操作，從而提高效能。
  2. 批量更新減少了回流和重繪操作。
• 挑戰：
  1. 大型 DOM 仍然會導致效能問題。
  2. 複雜的協調在計算上可能會很昂貴。

反應本機

傳統建築：

• 優點：
  1. 直接對應到本機元件可提供接近本機的效能。
  2. C 中的影子樹可實現高效的佈局計算。
• 挑戰：
  1. 橋樑通訊可能成為複雜互動的瓶頸。
  2. 大型清單或複雜的動畫可能需要額外的最佳化。

新架構：

• Advantages:
  1. Fabric allows for more synchronous operations, reducing bridge-related bottlenecks.
  2. TurboModules provide lazy loading and more efficient native module interactions.
  3. Improved type safety and potential for better performance optimizations.
• Challenges:
  1. Migration from the old architecture may require significant effort for existing apps.
  2. Developers need to learn new concepts and potentially update their coding practices.

Developer Experience and Tooling

React JS

• Familiar web development paradigms and tools.
• Rich ecosystem of web-specific libraries and frameworks.
• Browser DevTools for debugging and performance profiling.

React Native

Traditional Architecture:

• Requires understanding of mobile development concepts.
• Platform-specific APIs and components need separate handling.
• Custom tooling like React Native Debugger and platform-specific profilers.

New Architecture:

• Introduces new concepts like Fabric and TurboModules that developers need to understand.
• Improved type safety with CodeGen for better developer experience.
• Enhanced debugging capabilities, especially for native module interactions.

Code Reusability and Cross-Platform Development

Shared Concepts

Both React JS and React Native share core concepts:

• Component-based architecture
• Unidirectional data flow
• Virtual representation of the UI

Divergences

1. UI Components:

   • React JS uses HTML elements and CSS for styling.
   • React Native uses platform-specific components and a subset of CSS properties.

2. Event Handling:

   • React JS: DOM events (e.g., onClick, onChange)
   • React Native: Touch events (e.g., onPress) and custom APIs

3. Layout:

   • React JS: Flexbox, CSS Grid, and traditional CSS layouts
   • React Native: Primarily Flexbox with some limitations

4. Native Functionality:

   • React JS: Limited to web APIs and browser capabilities.
   • React Native: Access to platform-specific APIs, enhanced with TurboModules in the new architecture.

Example of divergence in layout:

<p>// React JS<br>
<div style={{ display: 'flex', justifyContent: 'center' }}><br>
  <span>Centered Content</span><br>
</div></p>

<p>// React Native (both architectures)<br>
import { View, Text } from 'react-native';</p>

<p><View style={{ flex: 1, justifyContent: 'center', alignItems: 'center' }}><br>
  <Text>Centered Content</Text><br>
</View></p>

Implications for Application Architecture

React JS

• Can leverage existing web APIs and browser capabilities.
• SEO considerations may influence component structure.
• Progressive enhancement and accessibility are key concerns.

React Native

Traditional Architecture:

• Must consider platform-specific capabilities and limitations.
• Performance optimization often involves native modules or platform-specific code.
• UI consistency across platforms requires careful component design.

New Architecture:

• Allows for more efficient bridge communication, potentially simplifying complex interactions.
• TurboModules enable more granular control over native module loading and execution.
• Fabric's synchronous layout capabilities may influence component design and animation strategies.

Conclusion

The architectural differences between React JS and React Native reflect their distinct target environments. React JS manipulates the DOM for web browsers, while React Native interacts with native components on mobile platforms. React Native's new architecture with Fabric and TurboModules represents a significant evolution, addressing performance bottlenecks and enhancing developer experience.

Understanding these differences is crucial for developers working across platforms or deciding between web and native mobile development. Each approach offers unique advantages and challenges, and the choice between them should be based on project requirements, performance needs, and target audience.

As both technologies continue to evolve, we can expect further optimizations and potentially more convergence in development patterns, making it easier to build truly cross-platform applications with React technologies.

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