Suspense for Data Fetching

• Suspense 컴포넌트는 지연 적재가 발생할 때, fallback 렌더링
  • pending
    • throw → fallback ui
  • resolved
    • rerender → child component render
  • rejected
    • throw error → fallback 무시, ErorrBoundary로 전달
• 프라미스 던지기로 suspense 실행
• 클로저로 내부 변수 캡슐화, 참조

•   import React, {Suspense} from "react";
    
    function createResource(fetcher) {
      let status = 'pending';
      let result: any;
    
      const suspender = fetcher.then(
        (res) => {
          status = 'success';
          result = res;
        },
        (err) => {
          status = 'error';
          result = err;
        }
      );
    
      return {
        read() {
          if (status === 'pending') throw suspender;
          if (status === 'error') throw result;
          return result;
        }
      };
    }
    
    const userResource = createResource( fetch('https://jsonplaceholder.typicode.com/users/1')
        .then(res => res.json())
    );
    
    function User() {
      const user = userResource.read(); // 동기처럼 읽기
      return <div>Username: {user.name}</div>;
    }
    
    function App() {
      return (
      <ErrornBoundary fallback={} >
        <Suspense fallback={}>
          <User />
        </Suspense>
    </ErrorBoundary>
      );
    }

Retry version

•   import React, { useState, Suspense } from "react";
    
    // 1. createResource
    function createResource<T>(fetcher: Promise<T>) {
      let status = "pending";
      let result: T;
      let error: any;
    
      const suspender = fetcher.then(
        (res) => {
          status = "success";
          result = res;
        },
        (err) => {
          status = "error";
          error = err;
        }
      );
    
      return {
        read() {
          if (status === "pending") throw suspender;
          if (status === "error") throw error;
          return result;
        },
      };
    }
    
    // 2. ErrorBoundary
    class ErrorBoundary extends React.Component<
      { fallback?: React.ReactNode; onReset?: () => void },
      { hasError: boolean }
    > {
      constructor(props: any) {
        super(props);
        this.state = { hasError: false };
      }
    
      static getDerivedStateFromError() {
        return { hasError: true };
      }
    
      handleRetry = () => {
        this.setState({ hasError: false });
        this.props.onReset?.(); // 부모에 알림 → 리소스 갱신 트리거
      };
    
      render() {
        if (this.state.hasError) {
          return (
            <div>
              ❌ 에러 발생
              <button onClick={this.handleRetry}>🔁 다시 시도</button>
            </div>
          );
        }
    
        return this.props.children;
      }
    }
    
    // 3. User (Suspense에서 fetch read)
    function User({ resource }: { resource: ReturnType<typeof createResource> }) {
      const user = resource.read();
      return <div>👤 Username: {user.name}</div>;
    }
    
    // 4. App (리소스를 상태로 관리 → 재생성 가능)
    export default function App() {
      const createUserResource = () =>
        createResource(
          fetch("https://jsonplaceholder.typicode.com/users/1").then((res) => {
            if (!res.ok) throw new Error("유저 정보 가져오기 실패");
            return res.json();
          })
        );
    
      const [resource, setResource] = useState(createUserResource);
    
      return (
        <ErrorBoundary onReset={() => setResource(createUserResource())}>
          <Suspense fallback={<div>⏳ 로딩 중...</div>}>
            <User resource={resource} />
          </Suspense>
        </ErrorBoundary>
      );
    }