@sdxc/duration

Compile-time-checked duration strings, and the conversions from them to milliseconds and seconds.

Installation

npm add @sdxc/duration

parse() reports failures as a Result from @sdxc/result, which installs alongside this package.

Usage

Basic Example

import { toMs, toSeconds } from "@sdxc/duration";

toMs("5 minutes"); // 300000
toMs("30s"); // 30000
toMs(1500); // 1500 — a bare number is already milliseconds

toSeconds("1 hour"); // 3600
toSeconds("30 days"); // 2592000

toMs("5 minuts"); // Type error: "minuts" is not a unit

Accepting A Duration In Your Own API

Declare the parameter as DurationInput and convert once, so callers may pass either form and your function states its own unit exactly once.

import type { DurationInput } from "@sdxc/duration";

import { toSeconds } from "@sdxc/duration";

interface CacheOptions {
	ttl: DurationInput;
}

function write(key: string, value: string, options: CacheOptions) {
	return cache.set(key, value, { ttlSeconds: toSeconds(options.ttl) });
}

write("session", value, { ttl: "30 days" });
write("session", value, { ttl: 2_592_000_000 }); // still valid

Parsing Text That Arrives At Runtime

Configuration values and form fields are plain strings, where the compile-time type cannot help. parse() checks them and reports a failure.

import { parse } from "@sdxc/duration";
import { isFailure } from "@sdxc/result";

let result = parse(process.env.SESSION_LIFETIME ?? "");

if (isFailure(result)) {
	console.error(result.error.message); // Invalid duration: "7 dayz"
	return;
}

let lifetimeMs = result.data;

API

toMs(input: DurationInput): number

Convert a duration to milliseconds, the unit JavaScript time arithmetic and timers count in. A bare number passes through untouched. A value that reaches it behind a cast returns NaN; route runtime text through parse(), which reports why the text was rejected.

let timeout = toMs("5 minutes");
// same as
let timeout = 5 * 60 * 1000;

let backoff = toMs("250ms"); // 250
let expiresAt = new Date(Date.now() + toMs("1 hour"));

toSeconds(input: DurationInput): number

Convert a duration to whole seconds, the unit HTTP cache headers and platform TTLs count in. Rounds to the nearest second with halves rounding up, so 1500 becomes 2 and 1400 becomes 1. Anything under half a second rounds to 0, which most seconds-based APIs read as "no caching", so pass at least "1 second" when a TTL must be non-zero.

let ttl = toSeconds("1 week");
// same as
let ttl = Math.round((7 * 24 * 60 * 60 * 1000) / 1000);

let maxAge = toSeconds("5 minutes"); // 300
let ttl = toSeconds("1 week"); // 604800

parse(text: string): Result<number, InvalidDurationError>

Parse duration text into milliseconds, returning a Success<number> or a Failure<InvalidDurationError> naming the rejected text. It accepts exactly the forms DurationString allows, plus a bare amount read as milliseconds, with surrounding whitespace trimmed. The grammar mirrors the type: a long spelling takes its single space and a short alias takes none, so "5 m" and "5minutes" are failures.

parse("15 minutes"); // { status: "success", data: 900000 }
parse("900000"); // { status: "success", data: 900000 }
parse("15 minuts"); // { status: "failure", error: InvalidDurationError }

InvalidDurationError

Error describing text that fails the duration grammar. It arrives inside a Failure value.

• text: string - The rejected text, kept verbatim and untrimmed for diagnostics

• name: string - Always "InvalidDurationError"

• message: string - Invalid duration: "<text>", quoted so whitespace and empty strings stay visible in logs

Types

DurationString

type DurationString = `${bigint} ${DurationUnit}` | `${bigint}${DurationUnitShort}`;

A duration written as text: a whole amount plus a unit, either spelled out after a single space or abbreviated with no space. The amount placeholder is ${bigint} rather than ${number} so only whole amounts type-check.

DurationInput

type DurationInput = number | DurationString;

What a duration-taking API declares. A bare number is always milliseconds.

DurationUnit

A unit spelled out after a single space: millisecond, second, minute, hour, day, week, and the plural of each.

DurationUnitShort

A unit abbreviated with no space: ms, s, m, h, d, w.

Accepted Forms

An amount may be 0 or negative ("-5 minutes" is -300000). Rejected at compile time, and by parse() at runtime: fractional and exponent amounts ("1.5h", "5e3s"), unit-only text ("hour"), the other form's spacing ("5 m", "5minutes"), uppercase units ("30S"), leading zeros and plus signs ("05s", "+5s"), compound durations ("1 hour 30 minutes"), and months and years, which have no fixed length.

Pattern: One Unit Per Boundary

Convert at the boundary that consumes the value, not at the call site that writes it. The caller writes the duration once, and each boundary converts to the unit it needs.

import type { DurationInput } from "@sdxc/duration";

import { toMs, toSeconds } from "@sdxc/duration";

interface SessionOptions {
	lifetime: DurationInput;
}

function createSession(options: SessionOptions) {
	return {
		// a cookie's Max-Age counts seconds
		maxAge: toSeconds(options.lifetime),
		// Date arithmetic counts milliseconds
		expiresAt: new Date(Date.now() + toMs(options.lifetime)),
	};
}

createSession({ lifetime: "30 days" });

Pattern: Validating Configuration Once At Startup

Parse duration configuration where it is read, so a typo in an environment variable is reported by name instead of becoming a NaN timer far away.

import type { Result } from "@sdxc/result";

import { parse } from "@sdxc/duration";
import { failure, isFailure } from "@sdxc/result";

function readDuration(name: string, value: string): Result<number, Error> {
	let result = parse(value);
	if (isFailure(result)) return failure(new Error(`${name} is not a duration: ${value}`));
	return result;
}

let lifetime = readDuration("SESSION_LIFETIME", process.env.SESSION_LIFETIME ?? "");

Pattern: Strings In Code, Numbers In Storage

Duration strings are for code and configuration. Keep storage and wire formats numeric, so a stored value never depends on this package's grammar.

import type { DurationInput } from "@sdxc/duration";

import { toMs } from "@sdxc/duration";

async function schedule(job: string, delay: DurationInput) {
	// the column stores milliseconds, not "5 minutes"
	await db.jobs.insert({ job, runAfterMs: Date.now() + toMs(delay) });
}

await schedule("send-digest", "5 minutes");