CHAN.RUN

ensure

Type-safe errors without the boilerplate

@chan.run/ensure

Type-safe errors without the boilerplate. Make error contracts explicit with zero ceremony.

Why?

JavaScript error handling is broken by default. Functions throw, but callers have no idea what. @chan.run/ensure makes errors part of the contract — with zero friction.

Install

pnpm add @chan.run/ensure

Quick Start

import { defineError, ensure, tryAsync, match } from "@chan.run/ensure";

const NotFoundError = defineError("NotFoundError");

// Guard a nullable value — throws NotFoundError if null/undefined
const user = ensure(db.find(id), NotFoundError, `No user: ${id}`);

// Safe async execution — never rejects
const result = await tryAsync(() => fetchUser(id));

if (!result.ok) {
  match(result.error, {
    NotFoundError: (err) => respond(404, err.message),
    _: (err) => {
      throw err;
    },
  });
}

API

Export	Purpose
`ensure`	Assert non-null/undefined — class, string, or class+message
`EnsureError`	Built-in error for string-form ensure
`defineError`	Define a reusable typed error class
`fault()`	Throw a typed error with cause chaining
`trySync()`	Run sync code, return `{ ok, data/error }`
`tryAsync()`	Run async code, return `{ ok, data/error }`
`declares()`	Annotate a function's error surface
`match()`	Handle errors by type with a handler map
`combines()`	Compose error surfaces from declared functions
`toJSON()`	Serialize a fault error for JSON transport
`fromJSON()`	Reconstruct a fault error from JSON

See the full API reference and examples.

Environment Support

Environment	Supported
Node.js 18+	✅
Deno	✅
Bun	✅
Browser	✅
Cloudflare Workers	✅