useComputedStore Pattern Overview

Comprehensive guide to computed value patterns using useComputedStore for derived state, performance optimization, and reactive calculations.

Pattern Categories

Basic Computed Patterns

Fundamental patterns for computed values:

• Simple Derived State: Computing values from a single store
• Multi-Store Computations: Combining data from multiple stores
• Data Formatting: Converting raw data to display format
• String Concatenation: Combining multiple fields

Advanced Computed Patterns

Complex computation scenarios (see original useComputedStore-patterns.md):

• Conditional Computations: Dynamic calculations based on conditions
• Complex Object Transformations: Advanced data manipulation
• Chained Computations: Dependent computed values
• Computed Store Instances: Reusable computed store creation

Performance Optimization

Optimization techniques for computed values:

• Caching with Custom Keys: Efficient result caching
• Memoized Dependencies: Optimizing expensive computations
• Selective Updates: Controlling when computations run
• Comparison Strategies: Choosing the right comparison method

Async Computed Patterns

Asynchronous computation patterns:

• Basic Async Computation: Simple async derived values
• Complex Async Dependencies: Managing multiple async operations
• Loading States: Handling async computation states
• Error Handling: Managing async computation errors

Quick Reference

Basic Usage

const computedValue = useComputedStore(
  [store1, store2],           // Dependencies
  ([data1, data2]) => {       // Computation function
    return data1 + data2;
  }
);

With Options

const computedValue = useComputedStore(
  [store1, store2],
  ([data1, data2]) => data1 + data2,
  {
    comparison: 'shallow',     // Comparison strategy
    cacheKey: 'my-computation' // Custom cache key
  }
);

Common Use Cases

1. Data Formatting

const formattedUser = useComputedStore(
  [userStore],
  ([user]) => `${user.firstName} ${user.lastName}`
);

2. Cross-Store Calculations

const orderTotal = useComputedStore(
  [cartStore, discountStore],
  ([cart, discount]) => cart.total * (1 - discount.percentage)
);

3. Conditional Logic

const userPermissions = useComputedStore(
  [userStore, settingsStore],
  ([user, settings]) => {
    if (user.role === 'admin') return settings.adminPermissions;
    return settings.userPermissions;
  }
);

Performance Considerations

Optimization Priority

1. Use Basic Patterns First: Start with simple computations
2. Add Caching: Use custom keys for expensive computations
3. Optimize Dependencies: Minimize dependency array changes
4. Consider Async: Move expensive operations to async patterns

When to Split Computations

• Complex Logic: Break down into smaller, focused computations
• Multiple Outputs: Create separate computed values for different outputs
• Performance Issues: Split expensive operations into cached sub-computations
• Reusability: Extract common computations into reusable patterns

Error Handling

Safe Computations

Always handle potential errors in computation functions:

const safeComputation = useComputedStore(
  [dataStore],
  ([data]) => {
    try {
      return expensiveCalculation(data);
    } catch (error) {
      console.error('Computation failed:', error);
      return defaultValue;
    }
  }
);

Best Practices Summary

✅ Universal Do's

• Keep computation functions pure (no side effects)
• Use appropriate comparison strategies for performance
• Handle errors gracefully with fallback values
• Cache expensive computations with custom keys
• Use descriptive names for computed values

❌ Universal Avoid's

• Performing side effects in computation functions
• Creating circular dependencies between computed values
• Ignoring error handling in computations
• Over-computing simple data access
• Complex nested computations without optimization

Related Patterns

• Basic Computed Patterns - Start here for fundamental patterns
• useStoreValue Patterns - Basic subscription patterns
• Memoization Patterns - Performance optimization
• Error Handling & Recovery - Robust error handling

Migration Guide

From Full Document

The comprehensive useComputedStore-patterns.md contains all patterns in detail. Use this overview to navigate to specific sections:

• Getting Started: Basic Computed Patterns
• Complex Scenarios: Original document sections 86-518
• Async Operations: Original document sections 519-710
• Real Examples: Original document sections 711-1091
• Error Handling: Original document sections 1092-1299