What is fdu?

fdu (faster date-time utility) is an ultra-fast, zero-dependency date manipulation library for TypeScript and JavaScript.

Why fdu?

⚡ Ultra-Fast

Built for speed, delivering ~4× faster performance than Day.js:

• 12× faster comparisons
• 6× faster chained operations
• 4× faster date manipulation
• 2× faster formatting

See benchmarks →

🕐 Temporally Correct

fdu implements time based on how humans actually perceive it:

• Floor Semantics: Time differences represent fully elapsed units (1.9 hours → 1 hour)
• Calendar Arithmetic: Months/years count calendar boundaries, not duration
• Temporal Direction: Earlier < later, negative = past
• Human-Centric Years: Year 0 = Year 0 (ISO 8601)

Read the philosophy →

💪 TypeScript-First

Unlike libraries where TypeScript types are added later, fdu is designed in TypeScript from day one:

• Full type inference for all operations
• Strict null safety
• IntelliSense support everywhere
• No @types/* package needed

🧭 Immutable & Predictable

Every operation returns a new instance, preventing unexpected mutations:

const date = fdu("2025-10-05");
const tomorrow = date.add(1, "day");

console.log(date.format("YYYY-MM-DD")); // '2025-10-05' (unchanged)
console.log(tomorrow.format("YYYY-MM-DD")); // '2025-10-06'

⚙️ Zero Dependencies

No external dependencies means:

• Smaller bundle size - No transitive dependencies
• Better security - Fewer attack vectors
• Faster installs - No dependency resolution
• More reliable - No breaking changes from dependencies

🧩 Tree-Shakeable

Modern ESM design ensures you only bundle what you use:

// Only imports what you need
import { fdu } from "@pyyupsk/fdu";
import { es } from "@pyyupsk/fdu/locale/es";
import { relativeTime } from "@pyyupsk/fdu/plugins/relative-time";

Design Principles

1. Temporal correctness first - Aligned with human time perception
2. Performance - Fast operations through correct algorithms
3. Type safety - Catch errors at compile time
4. Immutability - Predictable behavior
5. Zero dependencies - Stay lean and secure