Safe TypeScript

Build highly predictable, robust, and performant TypeScript/Node.js applications with a "zero technical debt" policy.

Retrieval-First Development

Always verify standards against the reference documentation before implementing.

Review the relevant documentation when writing new logic or performing code reviews.

When to Use

• Writing new TypeScript logic from scratch
• Refactoring existing TS/JS code to improve safety, performance, or memory stability
• Reviewing PRs for code quality and strict compiler standard adherence
• Optimizing memory allocations or V8 hot paths (e.g., GC pause mitigation)
• Implementing strict error handling without throw / try-catch

Reference Documentation

• ./references/safety.md - Control flow limits, bounded Promises, assertions, Result types
• ./references/performance.md - Object pools, TypedArrays, monomorphic shapes
• ./references/dx.md - Naming conventions, options structs, strict compiler flags, zero dependencies

Search: no recursion, AbortSignal, ObjectPool, Result<T,E>, noUncheckedIndexedAccess, Zod

Core Principles

Apply Safe TypeScript For

Do NOT Use

• Unbounded while(true) loops or Promises without timeouts
• Dynamic memory allocations (new Object(), [], {}) inside hot paths (triggers GC pauses)
• Unchecked array indices or implicit any types
• Expected control flow via throw and catch (Exceptions are for bugs/panics only)
• Proxy, Reflect, or runtime decorator magic

Quick Reference

Bounded Asynchronous Pattern (No Leaked Promises)

// Always bound asynchronous operations with a timeout
async function fetchWithBounds(url: string, timeoutMs: number): Promise<Result<Response, Error>> {
    const controller = new AbortController();
    const timeoutId = setTimeout(() => controller.abort(new Error("Timeout")), timeoutMs);
    
    try {
        const res = await fetch(url, { signal: controller.signal });
        if (!res.ok) return { ok: false, error: new Error(`HTTP ${res.status}`) };
        return { ok: true, value: res };
    } catch (err) {
        // Only catch native exceptions/abort errors to wrap them into Results
        return { ok: false, error: err instanceof Error ? err : new Error(String(err)) };
    } finally {
        clearTimeout(timeoutId);
    }
}

Allocation-Free Hot Path (Object Pooling)

// Pre-allocate at startup to avoid GC pauses during execution
class BufferPool {
    private pool: Uint8Array[];
    
    constructor(size: number, bufferSize: number) {
        this.pool = Array.from({ length: size }, () => new Uint8Array(bufferSize));
    }
    
    acquire(): Uint8Array | null {
        return this.pool.pop() || null;
    }
    
    release(buf: Uint8Array): void {
        // Reset state before returning to pool
        buf.fill(0);
        this.pool.push(buf);
    }
}

const pool = new BufferPool(100, 1024);

function processData(target: Uint8Array): Result<void, Error> {
    // Acquire from pool instead of `new Uint8Array(1024)`
    const buf = pool.acquire();
    if (!buf) return { ok: false, error: new Error("Pool exhausted") };

    try {
        // ... mutate target or buf in-place
        return { ok: true, value: undefined };
    } finally {
        pool.release(buf);
    }
}

Result Types over Exceptions

// Define explicit union returns instead of throwing
type Result<T, E = Error> = 
  | { ok: true; value: T }
  | { ok: false; error: E };

function parseData(input: string): Result<ParsedData, ValidationError> {
    if (!input) return { ok: false, error: new ValidationError("Empty input") };
    
    // ...
    return { ok: true, value: data };
}

Critical Rules

1. No Recursion - Keep control flow simple and execution bounds completely static.
2. Fixed Upper Bounds - All loops, arrays, and Promises must be bounded (e.g., by size or timeouts).
3. No Dynamic Memory After Init - Allocate all significant memory (Object Pools/Arrays) at startup.
4. Short Functions - Hard limit of 70 lines per function. Push ifs up, push fors down.
5. Check All Returns - Never ignore the result of a Result<T, E> or a Promise. Await everything.
6. Explicit Panics Only - throw only for programmer errors/broken invariants (like assertion failures). Use standard explicit Result returns for operational issues.
7. Strict Compilation - Must use strict: true, noUncheckedIndexedAccess: true, and noImplicitReturns: true.
8. Options Interfaces - Use explicit options interfaces for configuration instead of multiple boolean/primitive arguments.
9. Zero Dependencies - Strictly avoid third-party NPM dependencies outside standard library tools or extensively vetted utilities (like zod).
10. Strict Naming - Add units or qualifiers at the end of variables (e.g., timeoutMs, latencyMaxMs).

Anti-Patterns (NEVER)

• Using any or explicit type assertions (as Type) to bypass the compiler
• Throwing exceptions for expected business logic errors (e.g., throw new Error("Invalid User"))
• Using unbounded while(true) loops or new Promise(() => {}) without a reject mechanism
• Accessing arrays without verifying the index exists (requires noUncheckedIndexedAccess)
• Returning implicitly or ignoring awaited variables (void myAsyncFunc())
• Magic metaprogramming (Proxy, Reflect, dynamically adding/deleting object properties delete obj.prop)

Credits

• TIGER_STYLE.md