feat: add Validator#is

src/validators/BaseValidator.ts

@@ -80,6 +80,10 @@ export abstract class BaseValidator<T> {
 		return this.constraints.reduce((v, constraint) => constraint.run(v).unwrap(), this.handle(value).unwrap()) as R;
 	}
 
+	public is<R extends T = T>(value: unknown): value is R {
+		return this.run(value).isOk();
+	}
+
 	/**
 	 * Sets if the validator should also run constraints or just do basic checks.
 	 * @param isValidationEnabled Whether this validator should be enabled or disabled. You can pass boolean or a function returning boolean which will be called just before parsing.

tests/validators/base.test.ts

@@ -2,6 +2,22 @@ import { CombinedError, ExpectedValidationError, Result, s, ValidationError } fr
 import { expectClonedValidator, expectError, expectModifiedClonedValidator } from '../common/macros/comparators';
 
 describe('BaseValidator', () => {
+	describe('is', () => {
+		test("GIVEN any value THEN it's narrowed to schema type", () => {
+			const predicate = s.string;
+
+			const value = 'Hello there' as string | null;
+			const is = predicate.is(value);
+
+			expect(is).toBe(true);
+			if (is) {
+				expect<string>(value);
+			} else {
+				expect<null>(value);
+			}
+		});
+	});
+
 	describe('optional', () => {
 		const optionalPredicate = s.string.optional;