Environment variables

Lyn reads and checks your environment variables once, in new Lyn(). If one is missing or invalid, the app doesn't start, so it can never run with a broken configuration.

Declaring variables

Each entry maps a key of your choice to a variable name and a type:

const app = new Lyn({
  env: {
    port:   { name: "PORT",    type: "number" },
    apiKey: { name: "API_KEY", type: "string" },
    debug:  { name: "DEBUG",   type: "boolean" },
  },
});

type	Accepted values	You get
"string"	any non-blank value	string
"number"	a number, spaces around it ignored (" 42 ", -1.5)	number
"boolean"	exactly true, false, 1 or 0	boolean

Every declared variable is required. A blank value (PORT=) counts as missing, so it can't silently become 0 or "".

NODE_ENV is always required, in addition to your own variables.

.env files

Bun loads .env, .env.local and .env.<NODE_ENV> automatically. Keep your values there.

Reading the values

The parsed values are on app.env, typed from your declaration:

app.env.port;     // number
app.env.debug;    // boolean
app.env.nodeEnv;  // string, the value of NODE_ENV
app.env.other;    // type error: not declared

When something is wrong

new Lyn() throws a LynEnvError that lists every problem at once:

LynEnvError: Invalid environment variables:
  - API_KEY: missing
  - PORT: expected a number

The values themselves are never printed, since they may be secrets. For the other rules on secrets, see Keep secrets secret.

Left uncaught, the error stops the process. You can also catch it:

import { Lyn, LynEnvError } from "@rouret/lyn";

try {
  new Lyn({ env: { port: { name: "PORT", type: "number" } } });
} catch (error) {
  if (error instanceof LynEnvError) reportToMonitoring(error.message);
  throw error;
}

Not supported yet

• Optional variables and default values.