Comprehensive TypeScript 7-compatible guide with 44 rules across 8 categories, covering compiler configuration, type-system performance, async code, modules, safety, and measured runtime optimization.
When to Apply
Reference these guidelines when:
- Configuring tsconfig.json for a new or existing project
- Writing complex type definitions or generics
- Optimizing async/await patterns and data fetching
- Organizing modules and managing imports
- Reviewing code for compilation or runtime performance
Rule Categories by Priority
| Priority | Category | Impact | Prefix |
|---|---|---|---|
| 1 | Type System Performance | CRITICAL | type- |
| 2 | Compiler Configuration | CRITICAL | tscfg- |
| 3 | Async Patterns | HIGH | async- |
| 4 | Module Organization | HIGH | module- |
| 5 | Type Safety Patterns | MEDIUM-HIGH | safety- |
| 6 | Memory Management | MEDIUM | mem- |
| 7 | Runtime Optimization | LOW-MEDIUM | runtime- |
| 8 | Advanced Patterns | LOW | advanced- |
Table of Contents
- Type System Performance — CRITICAL
- 1.1 Add Explicit Return Types to Exported Functions — CRITICAL (faster declaration emit)
- 1.2 Avoid Deeply Nested Generic Types — CRITICAL (prevents exponential instantiation cost)
- 1.3 Avoid Large Union Types — CRITICAL (quadratic O(n²) comparison cost)
- 1.4 Extract Conditional Types to Named Aliases — CRITICAL (enables compiler caching, prevents re-evaluation)
- 1.5 Limit Type Recursion Depth — CRITICAL (prevents exponential type expansion)
- 1.6 Prefer Interfaces Over Type Intersections — CRITICAL (faster type resolution)
- 1.7 Simplify Complex Mapped Types — CRITICAL (reduces type computation)
- Compiler Configuration — CRITICAL
- 2.1 Configure Include and Exclude Properly — CRITICAL (prevents scanning thousands of unnecessary files)
- 2.2 Enable Incremental Compilation — CRITICAL (faster rebuilds)
- 2.3 Choose skipLibCheck Deliberately — CRITICAL (faster compilation)
- 2.4 Enable strictFunctionTypes for Sound Function Assignments — CRITICAL (enables optimized variance checking)
- 2.5 Use isolatedModules for Single-File Transpilers — CRITICAL (faster transpilation with bundlers)
- 2.6 Use Project References for Large Codebases — CRITICAL (faster incremental builds)
- 2.7 Migrate TypeScript 7 Configuration Deliberately — CRITICAL
- Async Patterns — HIGH
- 3.1 Annotate Async Function Return Types — HIGH (prevents runtime errors, improves inference)
- 3.2 Avoid await Inside Loops — HIGH (scales linearly with the number of iterations)
- 3.3 Avoid Unnecessary async/await — HIGH (eliminates microtask queue overhead)
- 3.4 Defer await Until Value Is Needed — HIGH (enables implicit parallelization)
- 3.5 Use Promise.all for Independent Operations — HIGH (improvement in I/O-bound code)
- Module Organization — HIGH
- 4.1 Avoid Barrel File Imports — HIGH (import cost, larger bundles)
- 4.2 Avoid Circular Dependencies — HIGH (prevents runtime undefined errors and slow compilation)
- 4.3 Control @types Package Inclusion — HIGH (prevents type conflicts and reduces memory usage)
- 4.4 Use Dynamic Imports for Large Modules — HIGH (reduces initial bundle)
- 4.5 Use Type-Only Imports for Types — HIGH (eliminates runtime imports for type information)
- Type Safety Patterns — MEDIUM-HIGH
- 5.1 Enable strictNullChecks — MEDIUM-HIGH
- 5.2 Prefer unknown Over any — MEDIUM-HIGH
- 5.3 Use Assertion Functions for Validation — MEDIUM-HIGH
- 5.4 Use const Assertions for Literal Types — MEDIUM-HIGH
- 5.5 Use Exhaustive Checks for Union Types — MEDIUM-HIGH
- 5.6 Use Type Guards for Runtime Type Checking — MEDIUM-HIGH
- Memory Management — MEDIUM
- 6.1 Avoid Closure Memory Leaks — MEDIUM (prevents retained references in long-lived callbacks)
- 6.2 Avoid Global State Accumulation — MEDIUM (prevents unbounded memory growth)
- 6.3 Clean Up Event Listeners — MEDIUM (prevents unbounded memory growth)
- 6.4 Clear Timers and Intervals — MEDIUM (prevents callback retention and repeated execution)
- 6.5 Use WeakMap for Object Metadata — MEDIUM (prevents memory leaks, enables automatic cleanup)
- Runtime Optimization — LOW-MEDIUM
- 7.1 Avoid Object Spread in Hot Loops — LOW-MEDIUM
- 7.2 Hoist Loop-Invariant Work in Measured Hot Paths — LOW-MEDIUM
- 7.3 Prefer Native Array Methods Over Lodash — LOW-MEDIUM
- 7.4 Use for-of for Simple Iteration — LOW-MEDIUM
- 7.5 Use Modern String Methods — LOW-MEDIUM
- 7.6 Use Set/Map for O(1) Lookups — LOW-MEDIUM
- Advanced Patterns — LOW
- 8.1 Use Branded Types for Type-Safe IDs — LOW (prevents mixing incompatible ID types)
- 8.2 Use satisfies for Type Validation with Inference — LOW (prevents property access errors, enables reliable autocomplete)
- 8.3 Use Template Literal Types for String Patterns — LOW (prevents string format errors at compile time)
How to Use
Run in the project root first:
npx -y @pymodel/react-frontend-skills detect # installed vs. targeted versions
npx -y @pymodel/react-frontend-skills scan --skill typescript # deprecated APIs → rule IDs
Read references/<rule-id>.md for each rule above that matches the task and for each scan hit: why it matters, then incorrect vs. correct code.