feat: add (isNull, checkDomain) util function

README.md

@@ -47,10 +47,13 @@ const difference = numberUtil.subtract(10, 3); // 7
 // Validation utilities
 const isValid = validationUtil.checkEmail("user@example.com"); // true
 const isHttpUrl = validationUtil.checkHttpUrl("https://example.com"); // true
+const isDomain = validationUtil.checkDomain("example.com"); // true
 
 // Common utilities
 const empty = commonUtil.isEmpty(""); // true
 const notEmpty = commonUtil.isEmpty("hello"); // false
+const nullCheck = commonUtil.isNull(null); // true
+const notNull = commonUtil.isNull("hello"); // false
 
 // Cookie utilities
 cookieUtil.setCookie("theme", "dark");
@@ -78,10 +81,12 @@ const theme = cookieUtil.getCookie("theme");
 
 - `checkEmail(email: string): boolean` - Validates email format
 - `checkHttpUrl(url: string): boolean` - Validates HTTP/HTTPS URL format
+- `checkDomain(domain: string): boolean` - Validates domain name format
 
 ### CommonUtil
 
 - `isEmpty(value: unknown): boolean` - Checks if a value is empty (null, undefined, "", 0, [], {}, empty Set/Map, NaN, or invalid Date)
+- `isNull(value: unknown): value is null` - Type guard that checks if a value is null and narrows the type
 
 ### CookieUtil
 

package/commonUtil/index.ts

@@ -1 +1,2 @@
 export { default as isEmpty } from "./isEmpty";
+export { default as isNull } from "./isNull";

package/commonUtil/isNull/index.test.ts

@@ -0,0 +1,20 @@
+import { describe, expect, test } from "vitest";
+import isNull from ".";
+
+describe("isNull 유틸 함수 테스트", () => {
+  test("null이 들어오는 경우 true를 반환한다.", () => {
+    expect(isNull(null)).toBe(true);
+  });
+  test("undefined이 들어오는 경우 false를 반환한다.", () => {
+    expect(isNull(undefined)).toBe(false);
+  });
+  test("빈 문자열이 들어오는 경우 false를 반환한다.", () => {
+    expect(isNull("")).toBe(false);
+  });
+  test("공백 문자열이 들어오는 경우 false를 반환한다.", () => {
+    expect(isNull(" ")).toBe(false);
+  });
+  test("0이 들어오는 경우 false를 반환한다.", () => {
+    expect(isNull(0)).toBe(false);
+  });
+});

package/commonUtil/isNull/index.ts

@@ -0,0 +1,3 @@
+export default function isNull(value: unknown): value is null {
+  return value === null;
+}

package/validationUtil/checkDomain/index.test.ts

@@ -0,0 +1,16 @@
+import { describe, expect, test } from "vitest";
+import checkDomain from ".";
+
+describe("checkDomain 유틸 함수 테스트", () => {
+  test("유효한 도메인이 들어오는 경우 true를 반환한다.", () => {
+    expect(checkDomain("example.com")).toBe(true);
+    expect(checkDomain("sub.example.co.uk")).toBe(true);
+    expect(checkDomain("www.my-site123.org")).toBe(true);
+    expect(checkDomain("www.layerapp.io")).toBe(true);
+  });
+  test("유효하지 않은 도메인이 들어오는 경우 false를 반환한다.", () => {
+    expect(checkDomain("")).toBe(false);
+    expect(checkDomain("invalid_domain")).toBe(false);
+    expect(checkDomain("https://layerapp.io")).toBe(false);
+  });
+});

package/validationUtil/checkDomain/index.ts

@@ -0,0 +1,4 @@
+export default function checkDomain(domain: string): boolean {
+  const domainRegex = /^(?!:\/\/)([a-z0-9-]+\.)+[a-z]{2,}$/;
+  return domainRegex.test(domain);
+}

package/validationUtil/index.ts

@@ -1,2 +1,3 @@
 export { default as checkEmail } from "./checkEmail";
 export { default as checkHttpUrl } from "./checkHttpUrl";
+export { default as checkDomain } from "./checkDomain";