libpreflight

Fail fast at process start with product-authored errors — runtime-floor checks and required-config assertions before heavy imports resolve.

Usage

Import the side-effect entry as the first import in every published CLI entry script. The package has zero production dependencies, so ESM post-order evaluation guarantees the floor check runs before any sibling import body executes.

#!/usr/bin/env node
import "@forwardimpact/libpreflight/node22";

// the rest of the bin's imports

Under Node >=22 the import returns silently. Under Node <22 the process writes two lines to stderr and exits 1:

Error: This command requires Node.js 22 or later (running 20.11.0).
Install Node.js 22 (LTS) from https://nodejs.org/ and re-run.

The failure intercepts the bin before any heavy static import — including upstream packages whose constructors may raise their own runtime-floor errors — evaluates.

Testable helper

For unit tests, import the parameterised check:

import { check } from "@forwardimpact/libpreflight/check.js";

const mockProcess = {
  versions: { node: "20.11.0" },
  stderr: { write: (chunk) => { /* capture */ } },
  exit: (code) => { /* capture */ },
};
check(22, mockProcess);

Required-config assertion

Call assertNonEmpty(value, label) from server.js immediately after createServiceConfig to fail the process at startup if a required configuration value is empty. Empty means an empty string, an empty array, an empty Set, or undefined/null.

import { assertNonEmpty } from "@forwardimpact/libpreflight/assert-non-empty.js";

const config = createServiceConfig("svc", { link_completion_ticket_secret: "" });
assertNonEmpty(config.link_completion_ticket_secret, "link_completion_ticket_secret");

On failure the process writes Error: required configuration "<label>" is empty. to stderr and exits 1. A test injects a processObj exposing stderr.write and exit.

Why a side-effect import per floor

Encoding the floor in the subpath (./node22, future ./node24, …) keeps the import statement self-describing and lets a CI invariant cross-check the floor literal against the importing package's engines.node.