Lesson 16-Svelte Core Features Source Code Analysis

Reactive System Source Code

Automatic Dependency Tracking Implementation

Compile-Time Dependency Tracking:

// How the compiler analyzes dependencies
function analyzeDependencies(node) {
  const dependencies = new Set();
  
  // Traverse AST nodes to identify all referenced variables
  traverse(node, {
    Identifier(path) {
      if (path.isReferencedIdentifier()) {
        dependencies.add(path.node.name);
      }
    }
  });
  
  return Array.from(dependencies);
}

// Example of generated dependency tracking code
function count() {
  if ($$tracking) {
    $$deps[0] = ($$deps[0] || new Set()).add('count');
  }
  return /* computed expression */;
}

Runtime Dependency Collection:

// Runtime dependency tracking implementation
let $$tracking = false;
let $$deps = {}; // Stores dependencies for each effect

function $$track(effectId, fn) {
  $$tracking = true;
  $$deps[effectId] = new Set();
  
  try {
    const result = fn();
    return result;
  } finally {
    $$tracking = false;
  }
}

// Usage example
$$track(0, () => {
  const value = count(); // Automatically records dependency on count
  return value * 2;
});

$store Reactive Update Mechanism

Core Store Implementation:

// Writable store implementation
function writable(initialValue) {
  let value = initialValue;
  const subscribers = new Set();
  
  function set(newValue) {
    if (value !== newValue) {
      value = newValue;
      subscribers.forEach(sub => sub(value));
    }
  }
  
  function subscribe(runner) {
    subscribers.add(runner);
    runner(value); // Execute immediately
    
    return () => {
      subscribers.delete(runner);
    };
  }
  
  return { set, subscribe };
}

// Derived store implementation
function derived(stores, fn, initial) {
  let value = initial;
  let dirty = true;
  
  const unsubscribe = stores.subscribe(() => {
    dirty = true;
    $$triggerUpdate(() => {
      if (dirty) {
        value = fn(stores);
        dirty = false;
      }
    });
  });
  
  return {
    subscribe(runner) {
      $$triggerUpdate(() => runner(value));
      return unsubscribe;
    }
  };
}

Reactive Update Scheduler:

// Update scheduler implementation
let $$pending = false;
let $$queue = [];

function $$scheduleUpdate() {
  if ($$pending) return;
  $$pending = true;
  
  Promise.resolve().then(() => {
    $$flushUpdates();
  });
}

function $$flushUpdates() {
  while ($$queue.length) {
    const update = $$queue.shift();
    update();
  }
  $$pending = false;
}

function $$triggerUpdate(update) {
  $$queue.push(update);
  $$scheduleUpdate();
}

Derived State Implementation

Derived Store Source Code:

// Derived state implementation
function derived(stores, fn, initial) {
  let value = initial;
  let dirty = true;
  
  // Subscribe to all dependent stores
  const unsubscribe = stores.subscribe(() => {
    dirty = true;
    $$triggerUpdate(() => {
      if (dirty) {
        value = fn(stores);
        dirty = false;
      }
    });
  });
  
  return {
    subscribe(runner) {
     (C) // Execute runner immediately
      $$triggerUpdate(() => runner(value));
      
      // Return unsubscribe function
      return unsubscribe;
    }
  };
}

// Example of compiled derived store usage
$: doubled = count * 2; // Compiled as a derived store

Caching Optimization Strategy:

// Cached derived store
function cachedDerived(stores, fn, initial) {
  let value = initial;
  let dirty = true;
  let cache = null;
  
  const unsubscribe = stores.subscribe(() => {
    dirty = true;
    $$triggerUpdate(() => {
      if (dirty) {
        cache = fn(stores);
        value = cache;
        dirty = false;
      }
    });
  });
  
  return {
    subscribe(runner) {
      $$triggerUpdate(() => runner(value));
      return unsubscribe;
    },
    // Manually retrieve cached value
    get cachedValue() {
      return cache;
    }
  };
}

Reactive Performance Optimization

Lazy Computation Implementation:

// Lazy computed store
function lazyDerived(stores, fn, initial) {
  let value = initial;
  let dirty = true;
  let computed = false;
  
  const unsubscribe = stores.subscribe(() => {
    dirty = true;
  });
  
  return {
    subscribe(runner) {
      if (!computed && dirty) {
        value = fn(stores);
        dirty = false;
        computed = true;
      }
      $$triggerUpdate(() => runner(value));
      return unsubscribe;
    },
    // Force recomputation
    recompute() {
      value = fn(stores);
      dirty = false;
      computed = true;
    }
  };
}

Batch Update Optimization:

// Batch update implementation
let $$batchDepth = 0;
let $$batchQueue = [];

function $$startBatch() {
  $$batchDepth++;
}

function $$endBatch() {
  $$batchDepth--;
  if ($$batchDepth === 0) {
    $$flushUpdates();
  }
}

function $$batchedTriggerUpdate(update) {
  $$batchQueue.push(update);
  
  if ($$batchDepth === 0) {
    $$flushUpdates();
  } else if ($$batchQueue.length === 1) {
    // Delay execution, waiting for possible additional updates
    Promise.resolve().then(() => {
      if ($$batchDepth > 0) return;
      $$flushUpdates();
    });
  }
}

Compile-Time and Runtime Coordinated Optimization

Compile-Time Optimization Strategies:

  1. Static Analysis: Pre-analyze dependency relationships in code
  2. Dead Code Elimination: Remove unused code and variables
  3. Constant Hoisting: Lift constants to module scope

Runtime Optimization Strategies:

  1. Dependency Tracking: Precisely track which states are used
  2. Lazy Computation: Compute derived states only when needed
  3. Batch Updates: Combine multiple state updates

Coordinated Optimization Example:

// Compile-time analysis example
function analyzeComponent(code) {
  const dependencies = new Set();
  const ast = parse(code);
  
  traverse(ast, {
    Identifier(path) {
      if (path.isReferencedIdentifier()) {
        dependencies.add(path.node.name);
      }
    }
  });
  
  return {
    // Generate code with only necessary dependencies
    code: generateOptimizedCode(ast, dependencies),
    // Mark static parts
    staticAnalysis: getStaticAnalysis(ast)
  };
}

// Runtime optimization example
function createOptimizedComponent(analysis) {
  return function Component(props) {
    // Subscribe only to analyzed dependencies
    const storeSubscriptions = subscribeToDependencies(analysis.dependencies);
    
    // Use static HTML parts
    const staticHTML = analysis.staticHTML;
    
    // ...remaining component logic
  };
}

Component System Source Code

Component Creation and Rendering Process

Component Creation Process:

// Component factory function
function create_component(ctor) {
  let instance;
  let fragment;
  
  return {
    c() {
      // Create DOM fragment
      fragment = ctor.c();
    },
    m(target, anchor) {
      // Mount DOM
      fragment.m(target, anchor);
      
      // Initialize component instance
      if (!instance) {
        instance = new ctor({
          target,
          anchor
        });
      }
    },
    p(ctx, dirty) {
      // Update props
      fragment.p(ctx, dirty);
      
      // Update component state
      if (instance) {
        instance.$set(ctx);
      }
    },
    d(detaching) {
      // Destroy DOM
      fragment.d(detaching);
      
      // Destroy component instance
      if (detaching) {
        instance.$destroy();
        instance = null;
      }
    }
  };
}

Rendering Process Source Code:

// Render entry point
function render(component, target, props) {
  // 1. Create component instance
  const componentInstance = create_component(component);
  
  // 2. Create DOM fragment
  componentInstance.c();
  
  // 3. Mount to target
  componentInstance.m(target, null);
  
  // 4. Set initial props
  if (props) {
    componentInstance.$set(props);
  }
  
  return {
    destroy() {
      componentInstance.d(true);
    },
    update(newProps) {
      componentInstance.$set(newProps);
    }
  };
}

Component Communication Internal Implementation

Props Passing Mechanism:

// Props passing implementation
function create_component(ctor) {
  let instance;
  let props = {};
  
  return {
    c() {
      // Create DOM fragment
      fragment = ctor.c();
    },
    m(target, anchor) {
      // Mount DOM
      fragment.m(target, anchor);
      
      // Initialize component instance and pass props
      if (!instance) {
        instance = new ctor({
          target,
          anchor,
          props // Pass props
        });
      }
    },
    p(newProps, dirty) {
      // Update props
      props = { ...props, ...newProps };
      fragment.p(ctx, dirty);
      
      // Update component state
      if (instance) {
        instance.$set(props);
      }
    },
    d(detaching) {
      // Destroy DOM and instance
      fragment.d(detaching);
      if (detaching) {
        instance.$destroy();
        instance = null;
      }
    }
  };
}

Event System Implementation:

// Event handling implementation
function create_event_handler(node, event, handler) {
  const wrappedHandler = (e) => {
    // Add event modifier handling here if needed
    handler(e);
  };
  
  node.addEventListener(event, wrappedHandler);
  
  return () => {
    node.removeEventListener(event, wrappedHandler);
  };
}

// Usage in component
function create_component(ctor) {
  let handlers = [];
  
  return {
    c() {
      // Create DOM element
      const button = element('button');
      
      // Add event listener
      handlers.push(create_event_handler(button, 'click', () => {
        // Handle click event
      }));
    },
    d(detaching) {
      // Clean up event listeners
      handlers.forEach(unsubscribe => unsubscribe());
    }
  };
}

Slot Rendering and Updates

Slot Implementation Mechanism:

// Slot rendering implementation
function render_slots(slots, ctx) {
  const renderedSlots = {};
  
  for (const [name, slot] of Object.entries(slots)) {
    if (slot) {
      // Render slot content
      renderedSlots[name] = slot(ctx);
    }
  }
  
  return renderedSlots;
}

// Using slots in a component
function create_component(ctor) {
  let slots = {};
  
  return {
    c() {
      // Render default slot
      const defaultSlot = render_slots(ctor.$$.slots, ctor.$$.ctx);
      
      // Create DOM element and insert slot content
      const div = element('div');
      if (defaultSlot.default) {
        div.appendChild(defaultSlot.default);
      }
    },
    p(ctx, dirty) {
      // Update slot content
      slots = render_slots(ctor.$$.slots, ctx);
    },
    d(detaching) {
      // Clean up slot DOM
    }
  };
}

Scoped Slot Implementation:

// Scoped slot implementation
function render_scoped_slots(slots, ctx) {
  const renderedSlots = {};
  
  for (const [name, slot] of Object.entries(slots)) {
    if (slot) {
      // Pass current context to slot
      renderedSlots[name] = slot(ctx);
    }
  }
  
  return renderedSlots;
}

// Using scoped slots in a component
function create_component(ctor) {
  let slots = {};
  
  return {
    c() {
      // Render scoped slots
      const scopedSlots = render_scoped_slots(ctor.$$.scopedSlots, ctor.$$.ctx);
      
      // Create DOM element and insert slot content
      const div = element('div');
      if (scopedSlots.item) {
        div.appendChild(scopedSlots.item({
          item: ctor.$$.ctx.item
        }));
      }
    },
    p(ctx, dirty) {
      // Update scoped slot context
      slots = render_scoped_slots(ctor.$$.scopedSlots, ctx);
    },
    d(detaching) {
      // Clean up slot DOM
    }
  };
}

Dynamic Component Loading and Switching

Dynamic Component Implementation:

// Dynamic component loader
function dynamic_component(loader, props) {
  let component;
  let instance;
  
  return {
    c() {
      // Dynamically load component
      loader().then(ctor => {
        component = ctor;
        // Create component instance
        instance = create_component(ctor);
        instance.c();
      });
    },
    m(target, anchor) {
      if (instance) {
        instance.m(target, anchor);
      }
    },
    p(newProps, dirty) {
      if (instance) {
        instance.$set(newProps);
      }
    },
    d(detaching) {
      if (instance) {
        instance.d(detaching);
      }
    }
  };
}

// Using dynamic components in a component
function create_component(ctor) {
  let currentComponent;
  
  return {
    c() {
      // Initially load default component
      currentComponent = dynamic_component(() => import('./DefaultComponent.svelte'), {});
      currentComponent.c();
    },
    m(target, anchor) {
      currentComponent.m(target, anchor);
    },
    p(ctx, dirty) {
      // Switch component based on condition
      if (ctx.showSpecial && currentComponent.type !== SpecialComponent) {
        currentComponent.d(true);
        currentComponent = dynamic_component(() => import('./SpecialComponent.svelte'), ctx);
        currentComponent.c();
        currentComponent.m(target, anchor);
      } else if (!ctx.showSpecial && currentComponent.type !== DefaultComponent) {
        currentComponent.d(true);
        currentComponent = dynamic_component(() => import('./DefaultComponent.svelte'), ctx);
        currentComponent.c();
        currentComponent.m(target, anchor);
      } else if (currentComponent) {
        currentComponent.p(ctx, dirty);
      }
    },
    d(detaching) {
      if (currentComponent) {
        currentComponent.d(detaching);
      }
    }
  };
}

Component Performance Optimization

Code Splitting Implementation:

// Dynamic import for code splitting
function lazy_component(loader) {
  let componentPromise;
  let component;
  let instance;
  
  return {
    c() {
      // Load component on first render
      if (!componentPromise) {
        componentPromise = loader().then(ctor => {
          component = ctor;
          return ctor;
        });
      }
      
      // Create placeholder element
      const div = element('div');
      div.textContent = 'Loading...';
    },
    m(target, anchor) {
      // Render after component is loaded
      if (componentPromise) {
        componentPromise.then(ctor => {
          if (!instance) {
            instance = create_component(ctor);
            instance.c();
            instance.m(target, anchor);
          }
        });
      }
    },
    p(ctx, dirty) {
      if (instance) {
        instance.$set(ctx);
      }
    },
    d(detaching) {
      if (instance) {
        instance.d(detaching);
      }
    }
  };
}

Memoization Optimization:

// Memoized props handling
function memoize_props(fn, deps) {
  let cachedDeps;
  let cachedResult;
  
  return function(newDeps) {
    if (depsEqual(cachedDeps, newDeps)) {
      return cachedResult;
    }
    
    cachedDeps = newDeps;
    cachedResult = fn(newDeps);
    return cachedResult;
  };
}

// Usage in component
function create_component(ctor) {
  let memoizedProps;
  
  return {
    c() {
      // Initial render
    },
    p(ctx, dirty) {
      // Handle props with memoization
      const processedProps = memoizedProps(ctx.props);
      fragment.p(processedProps, dirty);
    },
    d(detaching) {
      // Cleanup
    }
  };
}

Animation System Source Code

Animation Compilation and Implementation

Transition Compilation Implementation:

// Compile transition directive
function compile_transition(node, directive) {
  const { name, args } = parse_directive(directive);
  
  // Generate animation code
  return `
    const ${name}_transition = ${name}(${args});
    ${name}_transition.start();
    
    onDestroy(() => {
      ${name}_transition.end();
    });
  `;
}

// Runtime transition implementation
function fade(node, { duration = 400, easing = cubicOut } = {}) {
  const o = +getComputedStyle(node).opacity;
  
  return {
    duration,
    easing,
    css: t => `opacity: ${t * o}`
  };
}

// Usage in component
function create_fragment(ctx) {
  let div;
  
  return {
    c() {
      div = element('div');
      // Apply transition
      fade_transition = fade(div, { duration: 500 });
      fade_transition.start();
    },
    m(target, anchor) {
      insert(target, div, anchor);
    },
    p(ctx, dirty) {
      // Update animation parameters
      if (dirty & /*fade*/ 2) {
        fade_transition.set({ duration: /*newDuration*/ 300 });
      }
    },
    d(detaching) {
      if (detaching) {
        fade_transition.end();
        detach(div);
      }
    }
  };
}

Animate Compilation Implementation:

// Compile animate directive
function compile_animate(node, directive) {
  const { name, args } = parse_directive(directive);
  
  // Generate animation code
  return `
    const ${name}_animation = ${name}(${args});
    ${name}_animation.start();
  `;
}

// Runtime animate implementation
function fly(node, { x = 0, y = 0, duration = 400, easing = cubicOut } = {}) {
  const style = getComputedStyle(node);
  const target_x = x + parseFloat(style.transform?.replace(/[^0-9.-]/g, '') || 0);
  const target_y = y + parseFloat(style.transform?.replace(/[^0-9.-]/g, '') || 0);
  
  const start_x = parseFloat(style.transform?.replace(/[^0-9.-]/g, '') || 0);
  const start_y = parseFloat(style.transform?.replace(/[^0-9.-]/g, '') || 0);
  
  return {
    duration,
    easing,
    css: t => `
      transform: 
        translate(${(1 - t) * start_x + t * target_x}px, 
                  ${(1 - t) * start_y + t * target_y}px)
    `
  };
}

// Usage in component
function create_fragment(ctx) {
  let div;
  
  return {
    c() {
      div = element('div');
      // Apply animate
      fly_animation = fly(div, { x: 100, y: 50, duration: 600 });
      fly_animation.start();
    },
    m(target, anchor) {
      insert(target, div, anchor);
    },
    d(detaching) {
      // Animate does not require manual ending
      detach(div);
    }
  };
}

Core Animation Scheduling Logic

Timeline Implementation:

// Timeline scheduler
class Timeline {
  constructor() {
    this.animations = [];
    this.startTime = null;
  }
  
  add(animation) {
    this.animations.push(animation);
  }
  
  start() {
    this.startTime = performance.now();
    this._tick();
  }
  
  _tick() {
    const now = performance.now();
    const elapsed = now - this.startTime;
    
    let allFinished = true;
    
    for (const animation of this.animations) {
      if (elapsed < animation.duration) {
        allFinished = false;
        const progress = elapsed / animation.duration;
        animation.update(animation.easing(progress));
      } else {
        animation.update(1); // Ensure final state
      }
    }
    
    if (!allFinished) {
      requestAnimationFrame(() => this._tick());
    } else {
      this.complete();
    }
  }
  
  complete() {
    // Callback after all animations complete
  }
}

// Usage example
const timeline = new Timeline();
timeline.add(fadeAnimation);
timeline.add(flyAnimation);
timeline.start();

Staggered Animation Implementation:

// Staggered animation scheduler
function stagger(animations, { delay = 0, from = 'start' }) {
  return {
    start() {
      let currentDelay = 0;
      
      animations.forEach((animation, i) => {
        const staggerDelay = calculateStaggerDelay(i, animations.length, from, delay);
        setTimeout(() => {
          animation.start();
        }, currentDelay + staggerDelay);
        
        currentDelay += staggerDelay;
      });
    }
  };
}

function calculateStaggerDelay(index, total, from, baseDelay) {
  switch (from) {
    case 'start':
      return index * baseDelay;
    case 'center':
      return Math.abs(index - total / 2) * baseDelay;
    case 'end':
      return (total - index - 1) * baseDelay;
    default:
      return index * baseDelay;
  }
}

// Usage example
const staggeredAnimations = stagger([anim1, anim2, anim3], { delay: 50, from: 'center' });
staggeredAnimations.start();

Animation Performance Optimization Source Code

Hardware Acceleration Optimization:

// Force hardware-accelerated animation
function hardwareAccelerated(animation) {
  return {
    ...animation,
    css: t => `
      ${animation.css(t)}
      transform: translateZ(0); /* Force hardware acceleration */
    `
  };
}

// Optimized fade animation
function optimizedFade(node, options) {
  const o = +getComputedStyle(node).opacity;
  
  return hardwareAccelerated({
    duration: options.duration || 400,
    easing: options.easing || cubicOut,
    css: t => `opacity: ${t * o}`
  });
}

Reducing Repaints Optimization:

// Animation strategy to reduce repaints
function minimizeRepaint(animation) {
  let lastValue;
  
  return {
    ...animation,
    update(progress) {
      const currentValue = animation.css(progress);
      if (currentValue !== lastValue) {
        applyStyles(animation.node, currentValue);
        lastValue = currentValue;
      }
    }
  };
}

// Usage example
const optimizedAnimation = minimizeRepaint(fade(node, { duration: 500 }));
optimizedAnimation.start();

Compound Animation Optimization:

// Compound animation optimizer
function optimizeCompoundAnimations(animations) {
  // 1. Merge animations sharing the same properties
  const mergedAnimations = mergeSimilarAnimations(animations);
  
  // 2. Batch animations for the same element
  const batchedAnimations = batchElementAnimations(mergedAnimations);
  
  // 3. Parallelize animations that can run concurrently
  const parallelizedAnimations = parallelizeAnimations(batchedAnimations);
  
  return parallelizedAnimations;
}

// Usage example
const complexAnimations = [
  fade(node1, { duration: 500 }),
  fly(node1, { x: 100, duration: 600 }),
  fade(node2, { duration: 400 })
];

const optimized = optimizeCompoundAnimations(complexAnimations);
optimized.start();

Custom Animation Source Code Analysis

Custom Transition Implementation:

// Custom transition implementation
function create_custom_transition(name, implementation) {
  return function(node, params) {
    // Merge default and user parameters
    const options = { ...defaultOptions, ...params };
    
    // Return animation control object
    return {
      duration: options.duration,
      easing: options.easing,
      css: t => implementation.css(t, options),
      tick: t => implementation.tick(t, options)
    };
  };
}

// Usage example
const slide = create_custom_transition('slide', {
  css: (t, { direction }) => {
    const x = direction === 'left' ? 100 : -100;
    return `transform: translateX(${(1 - t) * x}px)`;
  },
  tick: (t, { onComplete }) => {
    if (t === 1) onComplete();
  }
});

// Usage in component
function create_fragment(ctx) {
  let div;
  
  return {
    c() {
      div = element('div');
      slide_transition = slide(div, { direction: 'left' });
      slide_transition.start();
    },
    m(target, anchor) {
      insert(target, div, anchor);
    },
    d(detaching) {
      slide_transition.end();
      detach(div);
    }
  };
}

Custom Animation Implementation:

// Custom animate implementation
function create_custom_animate(name, implementation) {
  return function(node, params) {
    // Merge default and user parameters
    const options = { ...defaultOptions, ...params };
    
    // Return animation control object
    return {
      duration: options.duration,
      easing: options.easing,
      start() {
        implementation.start(node, options);
      },
      end() {
        implementation.end(node, options);
      }
    };
  };
}

// Usage example
const bounce = create_custom_animate('bounce', {
  start(node, { height }) {
    // Implement bounce animation logic
    let currentHeight = height;
    let velocity = -height * 0.5;
    const gravity = 0.2;
    
    const animate = () => {
      velocity += gravity;
      currentHeight += velocity;
      
      if (currentHeight <= 0) {
        currentHeight = 0;
        velocity = 0;
      }
      
      node.style.height = `${currentHeight}px`;
      
      if (velocity !== 0) {
        requestAnimationFrame(animate);
      }
    };
    
    animate();
  },
  end(node) {
    node.style.height = '';
  }
});

// Usage in component
function create_fragment(ctx) {
  let div;
  
  return {
    c() {
      div = element('div');
      bounce_animation = bounce(div, { height: 100 });
      bounce_animation.start();
    },
    m(target, anchor) {
      insert(target, div, anchor);
    },
    d(detaching) {
      bounce_animation.end();
      detach(div);
    }
  };
}

Animation Accessibility and Compatibility

Accessibility Implementation:

// Accessibility-enhanced animation
function accessible_animation(animation, options) {
  return {
    ...animation,
    start() {
      // Check user preference for reduced motion
      if (prefersReducedMotion()) {
        // Apply final state immediately
        animation.css(1);
        if (animation.tick) animation.tick(1);
        if (options.onComplete) options.onComplete();
        return;
      }
      
      // Start animation normally
      animation.start();
    }
  };
}

// Detect user preference
function prefersReducedMotion() {
  return window.matchMedia('(prefers-reduced-motion: reduce)').matches;
}

// Usage example
const accessibleFade = accessible_animation(fade(node, { duration: 500 }), {
  onComplete() {
    console.log('Animation complete');
  }
});

accessibleFade.start();

Compatibility Handling:

// Compatibility shim implementation
function compatible_animation(animation) {
  // Detect browser support
  if (!supportsCssAnimations()) {
    // Fallback to JavaScript animation
    return {
      ...animation,
      css: () => '', // Disable CSS animation
      start() {
        // Implement JavaScript animation with requestAnimationFrame
        let start = null;
        
        const step = (timestamp) => {
          if (!start) start = timestamp;
          const progress = Math.min((timestamp - start) / animation.duration, 1);
          
          // Apply animation effect
          const styles = animation.css(progress);
          applyStyles(animation.node, styles);
          
          if (progress < 1) {
            requestAnimationFrame(step);
          } else if (animation.tick) {
            animation.tick(1);
          }
          
          if (progress === 1 && animation.onComplete) {
            animation.onComplete();
          }
        };
        
        requestAnimationFrame(step);
      }
    };
  }
  
  return animation;
}

// Detect CSS animation support
function supportsCssAnimations() {
  const style = document.createElement('div').style;
  return 'animation' in style || 'webkitAnimation' in style;
}

// Usage example
const compatibleFade = compatible_animation(fade(node, { duration: 500 }));
compatibleFade.start();

Fallback Strategy Implementation:

// Animation fallback strategy
function with_fallback(animation, fallback) {
  return {
    ...animation,
    start() {
      if (shouldUseFallback()) {
        // Use fallback scheme
        fallback.start();
      } else {
        // Use normal animation
        animation.start();
      }
    },
    end() {
      if (shouldUseFallback()) {
        fallback.end();
      } else {
        animation.end();
      }
    }
  };
}

// Determine if fallback is needed
function shouldUseFallback() {
  // 1. Detect performance
  if (isLowPerformanceDevice()) {
    return true;
  }
  
  // 2. Detect network conditions
  if (isSlowNetwork()) {
    return true;
  }
  
  // 3. Detect user preference
  if (prefersReducedMotion()) {
    return true;
  }
  
  return false;
}

// Usage example
const fadeWithFallback = with_fallback(
  fade(node, { duration: 500 }),
  simpleFade(node) // Simple opacity fade
);

fadeWithFallback.start();
Course: Svelte Family Deep Dive: Fast, Modern Web Development
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