validateNegativeInteger

Validates a value as a negative integer (less than zero).

This helper never throws and never mutates input. Returns a structured ValidationResult for composable validation pipelines.

Signature

function validateNegativeInteger(
    value: unknown,
    field: string
): ValidationResult<number>

Parameters

Name	Type	Description
value	unknown	The value to validate.
field	string	The field name for error reporting.

Returns

• { ok: true; value: number }: If valid.
• { ok: false; field: string; message: string }: If invalid.

Examples

validateNegativeInteger(-1, 'count');    // → { ok: true, value: -1 }
validateNegativeInteger(-42, 'total');  // → { ok: true, value: -42 }
validateNegativeInteger(0, 'zero');     // → { ok: false, field: 'zero', message: 'Value must be a negative integer' }
validateNegativeInteger(3, 'positive'); // → { ok: false, field: 'positive', message: 'Value must be a negative integer' }
validateNegativeInteger(-1.5, 'fraction'); // → { ok: false, field: 'fraction', message: 'Value must be a negative integer' }
validateNegativeInteger("5", 'stringVal'); // → { ok: false, field: 'stringVal', message: 'Value must be a negative integer' }

Notes

• Only integer number primitives less than zero are valid.
• Fractional numbers, zero, positive numbers, strings, NaN, Infinity, and non-numeric types fail.

Use normalizeNegativeInteger if input may be a string before validation.