feat: add isBoolean function

src/index.ts

@@ -23,6 +23,7 @@ import isArray from "./isArray";
 import isEmpty from "./isEmpty";
 import isNil from "./isNil";
 import isNumber from "./isNumber";
+import isBoolean from "./isBoolean";
 import isObject from "./isObject";
 import isString from "./isString";
 import isUndefined from "./isUndefined";
@@ -82,6 +83,7 @@ export {
   isEmpty,
   isNil,
   isNumber,
+  isBoolean,
   isObject,
   isString,
   isUndefined,

src/isBoolean.ts

@@ -0,0 +1,15 @@
+/**
+ * Returns true if `n` is a Boolean.
+ *
+ * @example
+ * ```ts
+ * isBoolean(true); // true
+ * isBoolean(null); // false
+ * isBoolean("FxTS"); // false
+ * ```
+ */
+function isBoolean(n: unknown): n is boolean {
+  return typeof n === "boolean";
+}
+
+export default isBoolean;

test/isBoolean.spec.ts

@@ -0,0 +1,16 @@
+import { isBoolean } from "../src/index";
+
+describe("isBoolean", function () {
+  it.each([undefined, null, 1, "1", Symbol("a"), () => null])(
+    "given non boolean then should return false",
+    function (s) {
+      const result = isBoolean(s);
+      expect(result).toEqual(false);
+    },
+  );
+
+  it("given boolean then should return true", function () {
+    const result = isBoolean(true);
+    expect(result).toEqual(true);
+  });
+});

type-check/isBoolean.test.ts

@@ -0,0 +1,14 @@
+import * as Test from "../src/types/Test";
+import { isBoolean, pipe } from "../src";
+
+const { checks, check } = Test;
+
+const res1 = isBoolean(true);
+const res2 = isBoolean("a");
+const res3 = pipe(true, isBoolean);
+
+checks([
+  check<typeof res1, boolean, Test.Pass>(),
+  check<typeof res2, boolean, Test.Pass>(),
+  check<typeof res3, boolean, Test.Pass>(),
+]);