feat: add isISO6391 decorator for language codes (#2626)

* Create isISO6391.ts

* Document `@IsIso6391()` in `README.md`

* Add unit tests

* Add `isISO6391` to exported decorators

---------

Co-authored-by: Brage Sekse Aarset <brage.aarset@gmail.com>

Author: RobinvanderVliet

README.md

@@ -918,6 +918,7 @@ isBoolean(value);
 | `@IsLatitude()`                                        | Checks if the string or number is a valid latitude coordinate.                                                                                                                                        |
 | `@IsLongitude()`                                       | Checks if the string or number is a valid longitude coordinate.                                                                                                                                       |
 | `@IsMobilePhone(locale: string)`                       | Checks if the string is a mobile phone number.                                                                                                                                                        |
+| `@IsISO6391()`                                         | Checks if the string is a valid ISO 639-1 officially assigned language code.                                                                                                                          |
 | `@IsISO31661Alpha2()`                                  | Checks if the string is a valid ISO 3166-1 alpha-2 officially assigned country code.                                                                                                                  |
 | `@IsISO31661Alpha3()`                                  | Checks if the string is a valid ISO 3166-1 alpha-3 officially assigned country code.                                                                                                                  |
 | `@IsISO31661Numeric()`                                 | Checks if the string is a valid ISO 3166-1 numeric officially assigned country code.                                                                                                                  |

src/decorator/decorators.ts

@@ -117,6 +117,7 @@ export * from './string/IsTimeZone';
 export * from './string/IsBase58';
 export * from './string/is-tax-id';
 export * from './string/is-iso4217-currency-code';
+export * from './string/isISO6391';
 
 // -------------------------------------------------------------------------
 // Type checkers

src/decorator/string/isISO6391.ts

@@ -0,0 +1,31 @@
+import { ValidationOptions } from '../ValidationOptions';
+import { buildMessage, ValidateBy } from '../common/ValidateBy';
+import isISO6391Validator from 'validator/lib/isISO6391';
+
+export const IS_ISO6391 = 'isISO6391';
+
+/**
+ * Check if the string is a valid [ISO 639-1](https://en.wikipedia.org/wiki/ISO_639-1) officially assigned language code.
+ */
+export function isISO6391(value: unknown): boolean {
+  return typeof value === 'string' && isISO6391Validator(value);
+}
+
+/**
+ * Check if the string is a valid [ISO 639-1](https://en.wikipedia.org/wiki/ISO_639-1) officially assigned language code.
+ */
+export function IsISO6391(validationOptions?: ValidationOptions): PropertyDecorator {
+  return ValidateBy(
+    {
+      name: IS_ISO6391,
+      validator: {
+        validate: (value, args): boolean => isISO6391(value),
+        defaultMessage: buildMessage(
+          eachPrefix => eachPrefix + '$property must be a valid ISO 639-1 language code',
+          validationOptions
+        ),
+      },
+    },
+    validationOptions
+  );
+}

test/functional/validation-functions-and-decorators.spec.ts

@@ -194,6 +194,7 @@ import {
   isTaxId,
   IsTaxId,
   IsISO4217CurrencyCode,
+  IsISO6391,
 } from '../../src/decorator/decorators';
 import { Validator } from '../../src/validation/Validator';
 import { ValidatorOptions } from '../../src/validation/ValidatorOptions';
@@ -5244,3 +5245,20 @@ describe('IsISO4217', () => {
     return checkInvalidValues(new MyClass(), invalidValues);
   });
 });
+
+describe('IsISO6391', () => {
+  class MyClass {
+    @IsISO6391()
+    someProperty: string;
+  }
+
+  it('should not fail for a valid ISO 639-1 language code', () => {
+    const validValues = ['de', 'en', 'eo', 'fy', 'nl'];
+    return checkValidValues(new MyClass(), validValues);
+  });
+
+  it('should fail for invalid values', () => {
+    const invalidValues = [undefined, null, '', 'FR', 'xx', 'tok'];
+    return checkInvalidValues(new MyClass(), invalidValues);
+  });
+});