Merge branch 'yousef-s-predicate-instance-of'

spec/predicates/isInstanceOf.spec.ts

@@ -0,0 +1,33 @@
+import 'mocha';
+import { given } from 'mocha-testdata';
+
+import { ensure, isInstanceOf, TinyType } from '../../src';
+import { expect } from '../expect';
+
+describe('predicates', () => {
+
+    /** @test {isInstanceOf} */
+    describe('::isInstanceOf', () => {
+        class Birthday extends TinyType {
+            constructor(public readonly value: Date) {
+                super();
+
+                ensure('Birthday', value, isInstanceOf(Date));
+            }
+        }
+
+        it('ensures that the argument is an instance of Date', () => {
+            expect(() => new Birthday(new Date())).to.not.throw;              // tslint:disable-line:no-unused-expression
+        });
+
+        given(
+            '2018-10-10',
+            undefined,
+            null,
+            {},
+            'string',
+        ).it('complains if the value does not meet the predicate', (value: any) => {
+            expect(() => new Birthday(value)).to.throw(`Birthday should be instance of Date`);
+        });
+    });
+});

src/predicates/index.ts

@@ -13,6 +13,7 @@ export * from './isLessThanOrEqualTo';
 export * from './isNumber';
 export * from './isOneOf';
 export * from './isString';
+export * from './isInstanceOf';
 export * from './or';
 export * from './Predicate';
 export * from './property';

src/predicates/isInstanceOf.ts

@@ -0,0 +1,20 @@
+import { Predicate } from './Predicate';
+
+/**
+ * @desc Ensures that the `value` is an instance of `type`
+ *
+ * @example
+ * import { ensure, isInstanceOf, TinyType } from 'tiny-types';
+ *
+ * class Birthday extends TinyType {
+ *     constructor(public readonly value: Date) {
+ *         ensure('Date', value, isInstanceOf(Date));
+ *     }
+ * }
+ *
+ * @param {Constructor<T>} type
+ * @returns {Predicate<T>}
+ */
+export function isInstanceOf<T>(type: { new (...args: any[]): T }): Predicate<T> {
+    return Predicate.to(`be instance of ${type.name}`, (value: T) => value instanceof type);
+}