sveltejs/kit · error · Error

Parameter values must be a string, number, boolean, or bigin

Error message

Parameter values must be a string, number, boolean, or bigint

What it means

`resolve_route` stringifies each parameter into the route path. Only strings, numbers, booleans, and bigints can be safely converted; any other value type (objects, arrays, null, undefined reaching this branch) is rejected with this error to prevent silently rendering `[object Object]` in URLs.

Source

Thrown at packages/kit/src/utils/routing.js:331

					if (typeof value === 'string') {
						if (value.startsWith('/') || value.endsWith('/')) {
							throw new Error(
								`Parameter '${name}' in route ${id} cannot start or end with a slash -- this would cause an invalid route like foo//bar`
							);
						}

						return value;
					}

					if (
						typeof value === 'number' ||
						typeof value === 'boolean' ||
						typeof value === 'bigint'
					) {
						return String(value);
					}

					throw new Error('Parameter values must be a string, number, boolean, or bigint');
				})
			)
			.filter(Boolean)
			.join('/') +
		(has_id_trailing_slash ? '/' : '')
	);
}

/**
 * @param {import('types').SSRNode} node
 * @returns {boolean}
 */
export function has_server_load(node) {
	return node.server?.load !== undefined || node.server?.trailingSlash !== undefined;
}

/**
 * Find the first route that matches the given path

View on GitHub (pinned to 03f1687fe6)

Solutions

1. Stringify or otherwise convert the value before resolving (e.g. `String(obj.id)`, `date.toISOString()`)
2. Ensure lookups that produce params cannot return null/undefined objects for required params
3. Coerce booleans/numbers deliberately so only intended primitives reach resolution

Example fix

// before
resolve_route(id, pattern, { date: new Date('2024-01-01') });
// after
resolve_route(id, pattern, { date: '2024-01-01' });

function isStringifiableParam(v) {
	return typeof v === 'string' || typeof v === 'number' || typeof v === 'boolean' || typeof v === 'bigint';
}
Object.values(params).forEach((v) => { if (!isStringifiableParam(v)) throw new Error('param not primitive'); });

function isParamValue(v) {
	return ['string', 'number', 'boolean', 'bigint'].includes(typeof v);
}

try {
	const href = resolveRoute(id, pattern, params);
} catch (e) {
	if (e.message.startsWith('Parameter values must be')) {
		// stringify/serialize the offending param before resolving
	}
	throw e;
}

When it happens

Trigger: Resolving a route with a params object containing an object/array (e.g. `{ id: { value: 1 } }`), null, or a value type not covered by the earlier branches (and not handled as optional/rest).

Common situations: Passing parsed objects (Date, model instances) as params instead of their string/id representation; accidentally wrapping the param in an object; supplying null from failed data lookups.

Related errors

• Missing parameter '${name}' in route ${id}
• Parameter '${name}' in route ${id} cannot start or end with
• Invalid param definition
• Missing params for dynamic route ID ${id}
• No matcher found for parameter '${name}'${file ? ` in ${file

AI-assisted analysis of sveltejs/kit@03f1687fe6 (2026-09-02). Data as JSON: /api/errors/0b4578f17931c2b1. Report an issue: GitHub.