control french postal code

frenchPostalCode.ts

export function validateFrenchPostalCode(
    input: string,
    partialControl = false
): boolean {
    // Check length constraints
    if (input.length > 5 || (!partialControl && input.length !== 5)) {
        return false;
    }

    const finalInput = input.toUpperCase();

    // Define valid French department codes
    const validDepartments = [
        ...Array.from({ length: 95 }, (_, i) => String(i + 1).padStart(2, '0')), // 01 to 95
        '2A',
        '2B', // Corsica
        '96',
        '97',
        '98', // Overseas territories
    ];

    // Validate based on length
    switch (finalInput.length) {
        case 1:
            // First character must be a digit between 0 and 9
            return /^[0-9]$/.test(finalInput);
        case 2:
            // First two characters must form a valid department code
            return validDepartments.includes(finalInput);
        case 3:
        case 4:
        case 5: {
            // First two characters must form a valid department code
            const departmentCode = finalInput.slice(0, 2);

            if (!validDepartments.includes(departmentCode)) {
                return false;
            }

            // Remaining characters must be digits
            const remainingPart = finalInput.slice(2);

            return /^[0-9]*$/.test(remainingPart);
        }
        default:
            return false;
    }
}

console.log(validateFrenchPostalCode('7')); // true
console.log(validateFrenchPostalCode('75')); // true
console.log(validateFrenchPostalCode('750')); // true
console.log(validateFrenchPostalCode('75008')); // true
console.log(validateFrenchPostalCode('750089')); // false
console.log(validateFrenchPostalCode('2A')); // true
console.log(validateFrenchPostalCode('2A1')); // true
console.log(validateFrenchPostalCode('2A100')); // true
console.log(validateFrenchPostalCode('2A1000')); // false