add: basic function with comments

src/totp.js

@@ -3,6 +3,61 @@
  *  @author   : Gin (gin.lance.inside@hotmail.com)
  */
 
- class TOTP {
-    
+import OTP from './otp';
+
+ class TOTP extends OTP {
+    /*＊
+     * @param {interval}
+     * @type {int} 
+     * @desc the time interval in seconds for OTP.
+     * This defaults to 30.
+     *
+     * @return {OTP}
+     */
+    constructor(interval=30, ...args) {
+        this.interval = interval;
+        super(...args);
+    }
+
+    /*＊
+     * Generate the OTP with current time.
+     *
+     * @return {OTP}
+     *
+     * @example
+     * ```javascript
+     * let totp = jsotp.TOTP.gen('BASE32_ENCODED_SECRET');
+     * totp.now(); // => 432143
+     * ```
+     */
+    now() {
+        console.log("TOTP.now");
+    }
+
+    /*＊
+     * Verifies the OTP passed in against the current time OTP.
+     *
+     * @param {otp}
+     * @type {String} 
+     * @desc the OTP waiting for checking
+     *
+     * @param {time}
+     * @type {int or datetime} 
+     * @desc Time to check OTP at (defaults to now)
+     *
+     * @return {Boolean}
+     *
+     * @example
+     * ```javascript
+     * let totp = jsotp.TOTP.gen('BASE32_ENCODED_SECRET');
+     * totp.now(); // => 432143
+     * // Verify for current time
+     * totp.verify(432143); // => true
+     * // Verify after 30s
+     * totp.verify(432143); // => false
+     * ```
+     */
+    verify(otp, time=null) {
+        console.log("TOTP.verify");
+    }
  }