Validation Utilities

Fast validators for emails, URLs, UUIDs, JSON strings, and TypeScript type guards in sc-fns/validation.

The sc-fns/validation module contains zero-dependency validators and strict TypeScript type guards.

ts
import {
    isEmail,
    isURL,
    isUUID,
    isJSON,
    isNumber,
    isString,
    isObject,
    isArray,
} from "sc-fns/validation";

`isEmail`

Validates email addresses using standard RFC 5322 pattern matching.

Signature

ts
function isEmail(value: unknown): value is string;

Examples

ts
isEmail("dev@sc-fns.org"); // true
isEmail("john.doe+tag@domain.co"); // true
isEmail("plainaddress"); // false
isEmail("missing@domain"); // false

`isURL`

Validates absolute web URLs using the native URL API. Supports custom protocol whitelists.

Signature

ts
function isURL(
    value: unknown,
    options?: {
        protocols?: string[]; // Default: ["http", "https"]
        requireProtocol?: boolean; // Default: true
    },
): value is string;

Examples

ts
isURL("https://turbo.build/repo"); // true
isURL("http://localhost:3000"); // true
isURL("ftp://files.example.com", { protocols: ["ftp", "http", "https"] }); // true
isURL("invalid-url"); // false

`isUUID`

Validates whether a string matches RFC 4122 UUID format (versions 1 through 5, or all).

Signature

ts
function isUUID(
    value: unknown,
    version?: 1 | 2 | 3 | 4 | 5 | "all", // Default: "all"
): value is string;

Examples

ts
isUUID("f47ac10b-58cc-4372-a567-0e02b2c3d479"); // true
isUUID("f47ac10b-58cc-4372-a567-0e02b2c3d479", 4); // true
isUUID("not-a-uuid"); // false

`isJSON`

Tests if a string is valid JSON syntax without crashing your process on parse failures.

Signature

ts
function isJSON(value: unknown): value is string;

Examples

ts
isJSON('{"name": "Alice", "role": "admin"}'); // true
isJSON("[1, 2, 3]"); // true
isJSON('{"invalid": json}'); // false

Type Guards: `isNumber`, `isString`, `isObject`, `isArray`

Strict TypeScript runtime guards that narrow unknown values safely.

ts
// isNumber guards against NaN and Infinity
isNumber(42); // true
isNumber(NaN); // false
isNumber(Infinity); // false
 
// isObject excludes arrays and null
isObject({ id: 1 }); // true
isObject([1, 2]); // false
isObject(null); // false
 
// isArray and isString
isArray(["a", "b"]); // true
isString("hello"); // true

How is this guide?

Last updated on October 25, 2026

Date Utilities

URL Utilities