feat: Add isSet type guard (silvermine#31)

src/index.ts

@@ -22,6 +22,7 @@ export * from './utils/is-number';
 export * from './utils/is-object';
 export * from './utils/is-promise';
 export * from './utils/is-promise-like';
+export * from './utils/is-set';
 export * from './utils/is-string';
 export * from './utils/is-undefined';
 export * from './utils/is-null';

src/utils/is-set.ts

@@ -0,0 +1,8 @@
+/**
+ * Type guard for `Set`s.
+ *
+ * @returns `true` if `o` is a `Set`, regardless of the types that it contains
+ */
+export function isSet(o: unknown): o is Set<unknown> {
+   return o instanceof Set;
+}

tests/utils/is-set.test.ts

@@ -0,0 +1,28 @@
+import { expect } from 'chai';
+import * as t from '../../src/index';
+
+
+describe('isSet', () => {
+
+   it('correctly classifies sets', () => {
+      expect(t.isSet(new Set([]))).to.strictlyEqual(true);
+      expect(t.isSet(new Set([ 'a', 'b', 'c' ]))).to.strictlyEqual(true);
+      expect(t.isSet(new Set([ 4 ]))).to.strictlyEqual(true);
+      expect(t.isSet(new Set([ 'a', 'b', 'c', 4 ]))).to.strictlyEqual(true);
+      expect(t.isSet(new Set())).to.strictlyEqual(true);
+   });
+
+   it('correctly classifies non-sets', () => {
+      expect(t.isSet([])).to.strictlyEqual(false);
+      expect(t.isSet({})).to.strictlyEqual(false);
+      expect(t.isSet(4)).to.strictlyEqual(false);
+      expect(t.isSet('')).to.strictlyEqual(false);
+      expect(t.isSet('a')).to.strictlyEqual(false);
+      expect(t.isSet(true)).to.strictlyEqual(false);
+      expect(t.isSet(undefined)).to.strictlyEqual(false);
+      expect(t.isSet(null)).to.strictlyEqual(false);
+      expect(t.isSet({ length: 0 })).to.strictlyEqual(false);
+      expect(t.isSet(() => {})).to.strictlyEqual(false);
+   });
+
+});