For AI agents: the complete documentation index is available at https://massaman.dev/llms.txt, the full documentation bundle is available at https://massaman.dev/llms-full.txt, and this page is available as Markdown at https://massaman.dev/index.md.
Install massaman
    v0.5.1 · MIT

    A rich blend of functional patterns.

    A functional TypeScript utility library with Rust-inspired Result types and exhaustive pattern matching, built on es-toolkit and ts-pattern.

    Install massamanBrowse the API
    Split TypeScript editor showing match and attemptAsync with Result handling
    built ones-toolkitts-patternTypeScript
    The good parts

    Small functions. Strong guarantees.

    Use the flat import surface or pull from focused subpaths. Every export tree-shakes.

    Errors are values
    Wrap unsafe work in Result and keep failure visible in the type.Learn more →
    Exhaustive matching
    Match typed patterns and let TypeScript catch every unhandled case.Learn more →
    Composable by default
    Build data flows from small functions instead of mutation and hidden state.Learn more →
    One utility surface
    Array, object, string, math, promise, and predicate helpers under one roof.Learn more →
    Types stay sharp
    Variadic predicates and type-level tests preserve inference through the pipeline.Learn more →
    Pay for what you import
    ESM-only, side-effect free, and split into focused public subpaths.Learn more →
    Result + pattern matching

    Handle failure as data.

    One task, written both ways. Assume fetchUser() throws a Response on HTTP failure.

    Exceptions, then manual narrowing

    The catch block receives unknown, so every branch has to re-establish what the failure was before it can say anything about it.

    • ✓message is a let, reassigned across branches
    • ✓unknown must be narrowed before the status is readable
    • ✓Nothing tells you when a case is missing
    let message: string

try {
  const user = await fetchUser(userId)
  message = `Welcome, ${user.name}`
} catch (error: unknown) {
  if (error instanceof Response) {
    if (error.status === 404) {
      message = 'User not found'
    } else if (error.status >= 500) {
      message = 'The service is unavailable'
    } else {
      message = `Request failed: ${error.status}`
    }
  } else if (error instanceof Error) {
    message = `Could not load user: ${error.message}`
  } else {
    message = `Could not load user: ${String(error)}`
  }
}

    Start with one function.

    Install massaman, import what you need, and keep the rest out of your bundle.

    Get startedView on GitHub