What causes "isBetween(): expected exactly two args" in n8n-io/n8n?

Supply exactly two date-typed arguments: `.isBetween($json.start, $json.end)`.

n8n-io/n8n · error · ExpressionExtensionError

isBetween(): expected exactly two args

Error message

isBetween(): expected exactly two args

What it means

The `.isBetween(a, b)` date extension checks whether the source date lies between two bounds. It throws when `extraArgs.length !== 2` because the body destructures exactly two values into `firstDate`/`secondDate`. Any other argument count is rejected up front.

Source

Thrown at packages/@n8n/expression-runtime/src/extensions/date-extensions.ts:151

	if (isDateTime(date)) return date.get(unit);

	return DateTime.fromJSDate(date).get(unit);
}

function format(date: Date | DateTime, extraArgs: unknown[]): string {
	const [dateFormat, localeOpts = {}] = extraArgs as [string, LocaleOptions];
	if (isDateTime(date)) {
		return date.toFormat(dateFormat, { ...localeOpts });
	}
	return DateTime.fromJSDate(date).toFormat(dateFormat, { ...localeOpts });
}

function isBetween(
	date: Date | DateTime,
	extraArgs: Array<string | Date | DateTime>,
): boolean | undefined {
	if (extraArgs.length !== 2) {
		throw new ExpressionExtensionError('isBetween(): expected exactly two args');
	}

	const [first, second] = extraArgs;

	const firstDate = convertToDateTime(first);
	const secondDate = convertToDateTime(second);

	if (!firstDate || !secondDate) {
		return;
	}

	if (firstDate > secondDate) {
		return secondDate < date && date < firstDate;
	}
	return secondDate > date && date > firstDate;
}

function isDst(date: Date | DateTime): boolean {

View on GitHub (pinned to 5ac6606e81)

Solutions

Supply exactly two date-typed arguments: `.isBetween($json.start, $json.end)`.
If you only need a one-sided comparison, switch to `.isAfter()` or `.isBefore()`.
Coerce bound arguments with `.toDateTime()` if they arrive as strings.

Example fix

// before
{{ $json.now.isBetween($json.start) }}
// after
{{ $json.now.isBetween($json.start, $json.end) }}

Defensive patterns

Strategy: validation

Validate before calling

// Ensure both bounds are present and date-like before the expression:
const { start, end } = $json;
if (start == null || end == null) {
  throw new Error('isBetween(): both start and end are required');
}
return $json;

Type guard

const isDateLike = (v: unknown): v is string | Date =>
  typeof v === 'string' || (v instanceof Date) || (v != null && typeof v === 'object' && 'toISO' in v);

Prevention

Count the arguments inside the parentheses — `.isBetween` needs exactly two.
Coerce bound arguments with `.toDateTime()` when they may arrive as strings.
Use `.isAfter()` / `.isBefore()` for one-sided comparisons.

When it happens

Trigger: Calling with a single bound: `.isBetween($json.start)`; with three: `.isBetween(a, b, c)`; or with none.

Common situations: Copying from `.isAfter()` / `.isBefore()` which take one argument; an optional second bound that was omitted because upstream data was missing.

Related errors

AI-assisted analysis of n8n-io/n8n@5ac6606e81 (2026-08-12). Data as JSON: /api/errors/824aa4000a44e2b4. Report an issue: GitHub.