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# Runtime Sprinkles
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Lightweight runtime version of sprinkles creation for dynamic styling without build-time constraints. Enables the use of sprinkles in environments where vanilla-extract's file scope is not available.
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## Capabilities
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### createSprinkles (Runtime)
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Runtime-only version of createSprinkles that works without vanilla-extract's file scope requirements. Perfect for testing environments, server-side rendering, or dynamic style generation.
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```typescript { .api }
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/**
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 * Creates a sprinkles function for runtime usage without file scope constraints
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 * @param args - Variable number of property configuration objects from defineProperties
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 * @returns SprinklesFn for runtime composition of CSS class names
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 */
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function createSprinkles<Args extends ReadonlyArray<SprinklesProperties>>(
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  ...args: Args
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): SprinklesFn<Args>;
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/**
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 * Same SprinklesFn type as build-time version but without CSS composition
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 */
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type SprinklesFn<Args extends ReadonlyArray<SprinklesProperties>> = ((
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  props: SprinkleProps<Args>
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) => string) & { properties: Set<keyof SprinkleProps<Args>> };
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```
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## Key Differences from Build-time Version
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1. **No CSS Generation**: Runtime sprinkles only look up pre-existing class names; they don't generate CSS
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2. **No File Scope Requirement**: Can be used outside of vanilla-extract's build-time file scope
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3. **Performance Optimized**: Lightweight runtime with minimal overhead (<0.5KB gzipped)
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4. **Class Name Composition**: Returns space-separated class name strings without CSS composition
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## Usage Examples
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**Basic runtime setup:**
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```typescript
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// This import works at runtime without build constraints
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import { createSprinkles } from "@vanilla-extract/sprinkles/createRuntimeSprinkles";
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// Use the same property definitions as build-time
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const responsiveProperties = defineProperties({
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  conditions: {
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    mobile: {},
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    tablet: { '@media': 'screen and (min-width: 768px)' },
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    desktop: { '@media': 'screen and (min-width: 1024px)' }
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  },
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  defaultCondition: 'mobile',
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  properties: {
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    display: ['none', 'flex', 'block'],
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    flexDirection: ['row', 'column'],
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    padding: {
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      small: '8px',
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      medium: '16px',
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      large: '24px'
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    }
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  }
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});
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// Create runtime sprinkles function
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const runtimeSprinkles = createSprinkles(responsiveProperties);
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```
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**Dynamic runtime styling:**
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```typescript
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import { createSprinkles } from "@vanilla-extract/sprinkles/createRuntimeSprinkles";
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// Runtime sprinkles for dynamic styling
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function createDynamicComponent(props: any) {
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  const className = runtimeSprinkles({
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    display: 'flex',
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    flexDirection: props.isColumn ? 'column' : 'row',
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    padding: props.size === 'large' ? 'large' : 'medium'
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  });
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  return `<div class="${className}">${props.children}</div>`;
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}
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// Usage with dynamic values
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const component1 = createDynamicComponent({
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  isColumn: true,
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  size: 'large',
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  children: 'Content'
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});
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const component2 = createDynamicComponent({
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  isColumn: false,
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  size: 'medium',
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  children: 'Other content'
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});
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```
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**Testing environments:**
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```typescript
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// jest.config.js or test setup
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import { createSprinkles } from "@vanilla-extract/sprinkles/createRuntimeSprinkles";
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// Mock sprinkles for testing without build-time constraints
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const mockSprinkles = createSprinkles(/* property definitions */);
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// Test component styling
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describe('Component styles', () => {
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  it('should generate correct class names', () => {
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    const className = mockSprinkles({
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      display: 'flex',
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      padding: 'medium'
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    });
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    expect(className).toContain('display_flex');
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    expect(className).toContain('paddingTop_medium');
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  });
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  it('should handle conditional values', () => {
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    const className = mockSprinkles({
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      flexDirection: {
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        mobile: 'column',
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        desktop: 'row'
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      }
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    });
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    expect(className).toContain('flexDirection_column_mobile');
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    expect(className).toContain('flexDirection_row_desktop');
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  });
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});
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```
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**Server-side rendering:**
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```typescript
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import { createSprinkles } from "@vanilla-extract/sprinkles/createRuntimeSprinkles";
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// Server-side component with runtime sprinkles
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function ServerComponent({ layout, spacing, theme }) {
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  const className = runtimeSprinkles({
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    display: 'flex',
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    flexDirection: layout === 'vertical' ? 'column' : 'row',
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    padding: spacing,
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    background: theme === 'dark' ? 'elevated' : 'surface'
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  });
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  return {
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    html: `<div class="${className}">Server-rendered content</div>`,
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    className: className
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  };
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}
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// Usage in server context
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const rendered = ServerComponent({
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  layout: 'vertical',
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  spacing: 'large',
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  theme: 'dark'
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});
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```
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**Conditional runtime composition:**
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```typescript
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import { createSprinkles } from "@vanilla-extract/sprinkles/createRuntimeSprinkles";
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// Runtime composition with conditional logic
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function createResponsiveLayout(config: {
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  isMobile: boolean;
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  isTablet: boolean;
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  isDesktop: boolean;
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  alignment: 'left' | 'center' | 'right';
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}) {
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  let flexDirection: 'row' | 'column' = 'row';
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  let justifyContent: string = 'flex-start';
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  if (config.isMobile) {
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    flexDirection = 'column';
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  }
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  switch (config.alignment) {
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    case 'center':
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      justifyContent = 'center';
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      break;
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    case 'right':
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      justifyContent = 'flex-end';
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      break;
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  }
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  return runtimeSprinkles({
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    display: 'flex',
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    flexDirection,
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    justifyContent
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  });
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}
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// Usage
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const mobileLayout = createResponsiveLayout({
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  isMobile: true,
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  isTablet: false,
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  isDesktop: false,
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  alignment: 'center'
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});
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```
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**Properties introspection at runtime:**
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```typescript
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import { createSprinkles } from "@vanilla-extract/sprinkles/createRuntimeSprinkles";
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const runtimeSprinkles = createSprinkles(/* properties */);
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// Same introspection API as build-time version
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console.log(runtimeSprinkles.properties.has('display')); // true
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console.log(runtimeSprinkles.properties.has('fontSize')); // false
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// Filter runtime props
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function filterSprinkleProps(props: Record<string, any>) {
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  const sprinkleProps: Record<string, any> = {};
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  const otherProps: Record<string, any> = {};
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  for (const [key, value] of Object.entries(props)) {
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    if (runtimeSprinkles.properties.has(key)) {
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      sprinkleProps[key] = value;
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    } else {
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      otherProps[key] = value;
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    }
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  }
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  return { sprinkleProps, otherProps };
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}
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// Usage
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const { sprinkleProps, otherProps } = filterSprinkleProps({
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  display: 'flex',
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  padding: 'medium',
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  onClick: () => {},
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  'data-testid': 'component'
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});
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const className = runtimeSprinkles(sprinkleProps);
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```
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**Error handling at runtime:**
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```typescript
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import { createSprinkles } from "@vanilla-extract/sprinkles/createRuntimeSprinkles";
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const runtimeSprinkles = createSprinkles(/* properties */);
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// Runtime error handling (development mode)
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try {
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  const className = runtimeSprinkles({
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    display: 'invalid-value' // Will throw SprinklesError in development
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  });
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} catch (error) {
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  if (error.name === 'SprinklesError') {
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    console.error('Sprinkles validation error:', error.message);
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    // Handle gracefully in production
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  }
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}
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// Safe runtime usage with fallbacks
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function safeRuntimeSprinkles(props: any, fallback = '') {
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  try {
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    return runtimeSprinkles(props);
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  } catch (error) {
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    if (process.env.NODE_ENV === 'development') {
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      console.warn('Sprinkles error:', error.message);
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    }
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    return fallback;
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  }
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}
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```
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## Performance Considerations
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- **Lightweight**: Runtime sprinkles adds minimal JavaScript overhead (<0.5KB gzipped)
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- **Pre-generated CSS**: All CSS classes are generated at build time; runtime only does lookups
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- **Caching**: Class name combinations are efficiently cached using LRU cache
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- **Tree Shaking**: Unused property configurations can be tree-shaken
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- **No Style Injection**: No runtime style injection or DOM manipulation
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### Build-time vs Runtime Performance
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**Build-time sprinkles:**
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- Zero runtime cost for style composition
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- CSS classes are composed at build time
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- Uses vanilla-extract's `composeStyles` for optimal CSS merging
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- File scope validation ensures correct usage
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**Runtime sprinkles:**
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- Minimal JavaScript overhead for class name concatenation
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- Uses simple string composition (`mockComposeStyles`)
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- No CSS composition - returns space-separated class names
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- Always validates class name lookup for safety
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### Memory Usage
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```typescript
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// Runtime sprinkles memory profile
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const runtimeSprinkles = createSprinkles(properties);
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// Memory used:
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// - Property definitions: ~1-5KB depending on configuration size  
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// - Function closure: ~200 bytes
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// - Properties Set: ~100 bytes per property
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// - Total: Usually <10KB for typical configurations
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```
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### Performance Benchmarks
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Typical performance characteristics:
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- **Class name lookup**: ~0.01ms per property
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- **Conditional value resolution**: ~0.05ms per conditional property
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- **Responsive array processing**: ~0.1ms per array
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- **String concatenation**: ~0.001ms per class name
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### Optimization Tips
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```typescript
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// ✓ Good: Reuse sprinkles functions
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const sprinkles = createSprinkles(properties);
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const class1 = sprinkles({ display: 'flex' });
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const class2 = sprinkles({ display: 'block' });
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// ✗ Avoid: Creating new sprinkles functions repeatedly
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function BadComponent() {
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  const sprinkles = createSprinkles(properties); // Recreated each render
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  return sprinkles({ display: 'flex' });
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}
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// ✓ Good: Memoize complex conditional values
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const memoizedStyle = useMemo(() => sprinkles({
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  display: complexCondition ? 'flex' : 'block',
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  padding: calculatePadding()
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}), [complexCondition, calculatePadding]);
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// ✓ Good: Batch class name generation
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const classes = {
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  container: sprinkles({ display: 'flex', padding: 'medium' }),
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  item: sprinkles({ flex: '1', margin: 'small' }),
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  button: sprinkles({ padding: 'small', border: 'none' })
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};
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```
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## Import Paths
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```typescript
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// Runtime sprinkles (no build-time CSS generation)
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import { createSprinkles } from "@vanilla-extract/sprinkles/createRuntimeSprinkles";
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// Build-time sprinkles (requires vanilla-extract file scope)
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import { createSprinkles } from "@vanilla-extract/sprinkles";
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```