Problems › TypeScript › validation
Normalise a phone number
People type phone numbers however they like. The CRM stores exactly one shape, so the importer either produces that shape or rejects the row.
- Throw away everything that is not a digit.
- A single leading zero is a national prefix and is dropped.
- What is left must be exactly ten digits.
- The country code must itself be one to three digits.
- The result is a plus sign, the country code, then the ten digits. Anything that does not fit gives null.
normalisePhone(raw: string, countryCode: string) → string?
Where you start
function normalisePhone(raw: string, countryCode: string): string | null {
}Worked examples
| Call | Result |
|---|---|
normalisePhone("0532 123 45 67", "90") | "+905321234567" |
normalisePhone("532-123-4567", "90") | "+905321234567" |
normalisePhone("(532) 123 45 67", "1") | "+15321234567" |
normalisePhone("123", "90") | null |
Hint
Clean, then drop the leading zero, then check the length. Three steps in that order.
Reference solution in TypeScript
function normalisePhone(raw: string, countryCode: string): string | null {
if (countryCode.length < 1 || countryCode.length > 3) return null;
for (const c of countryCode) if (c < '0' || c > '9') return null;
let d = '';
for (const c of raw) if (c >= '0' && c <= '9') d += c;
if (d.startsWith('0')) d = d.slice(1);
return d.length === 10 ? '+' + countryCode + d : null;
}