Add reusable validators - fixes #41 (#42)

source/index.ts

@@ -16,6 +16,12 @@ export type TypedArray = Int8Array | Uint8Array | Uint8ClampedArray | Int16Array
 
 export interface Ow {
 	<T>(value: T, predicate: Predicate<T>): void;
+	/**
+	 * Create a reusable validator.
+	 *
+	 * @param predicate Predicate used in the validator function.
+	 */
+	create<T>(predicate: Predicate<T>): (value: T) => void;
 	/**
 	 * Test the value to be a string.
 	 */
@@ -148,6 +154,9 @@ const main = <T>(value: T, predicate: Predicate<T>) => {
 };
 
 Object.defineProperties(main, {
+	create: {
+		value: <T>(predicate: Predicate<T>) => (value: T) => main(value, predicate)
+	},
 	string: {
 		get: () => new StringPredicate()
 	},

source/test/test.ts

@@ -7,3 +7,12 @@ test('not', t => {
 	t.notThrows(() => m('foo!', m.string.not.alphanumeric));
 	t.throws(() => m('' as any, m.string.not.empty), '[NOT] Expected string to be empty, got ``');
 });
+
+test('reusable validator', t => {
+	const checkUsername = m.create(m.string.minLength(3));
+
+	t.notThrows(() => checkUsername('foo'));
+	t.notThrows(() => checkUsername('foobar'));
+	t.throws(() => checkUsername('fo'), 'Expected string to have a minimum length of `3`, got `fo`');
+	t.throws(() => checkUsername(5 as any), 'Expected argument to be of type `string` but received type `number`');
+});