diff --git a/lib/add-v16.js b/lib/add-v16.js
new file mode 100644
index 0000000..40308b4
--- /dev/null
+++ b/lib/add-v16.js
@@ -0,0 +1,26 @@
+function add(firstNumber, secondNumber) {
+  const [shortNumber, longNumber] =
+    firstNumber.length < secondNumber.length
+      ? [firstNumber, secondNumber]
+      : [secondNumber, firstNumber];
+
+  let result = '';
+  let lastSumLargeThanTen = false;
+
+  for (let i = -1; i >= -shortNumber.length; i--) {
+    const sum = parseInt(shortNumber.at(i)) + parseInt(longNumber.at(i));
+
+    if (lastSumLargeThanTen) {
+      result = sum + parseInt(result.at(0)) + result.substring(1);
+    } else {
+      result = sum + result;
+    }
+    lastSumLargeThanTen = sum > 10;
+  }
+
+  return (
+    longNumber.substring(0, longNumber.length - shortNumber.length) + result
+  );
+}
+
+module.exports = add;
diff --git a/lib/add.js b/lib/add.js
index 1714b95..b69edd8 100644
--- a/lib/add.js
+++ b/lib/add.js
@@ -1,5 +1,28 @@
-function add() {
-  // 实现该函数
+function add(firstNumber, secondNumber) {
+  const [shortNumber, longNumber] =
+    firstNumber.length < secondNumber.length
+      ? [firstNumber, secondNumber]
+      : [secondNumber, firstNumber];
+
+  let result = '';
+  let lastSumLargeThanTen = false;
+
+  for (let i = shortNumber.length - 1; i >= 0; i--) {
+    const sum =
+      parseInt(shortNumber.substring(i, i + 1)) +
+      parseInt(longNumber.substring(i, i + 1));
+
+    if (lastSumLargeThanTen) {
+      result = sum + parseInt(result.substring(0, 1)) + result.substring(1);
+    } else {
+      result = sum + result;
+    }
+    lastSumLargeThanTen = sum > 10;
+  }
+
+  return (
+    longNumber.substring(0, longNumber.length - shortNumber.length) + result
+  );
 }
 
-module.exports = add
\ No newline at end of file
+module.exports = add;
diff --git a/test/test.spec.js b/test/test.spec.js
index 935b70e..ccdf10f 100644
--- a/test/test.spec.js
+++ b/test/test.spec.js
@@ -1,11 +1,14 @@
 var add = require('../lib/add')
+// var add = require('../lib/add-v16');
 
 describe('大数相加add方法', function () {
   test('字符串"42329"加上字符串"21532"等于"63861"', function () {
     expect(add('42329', '21532')).toBe('63861')
   })
-  
+
   test('"843529812342341234"加上"236124361425345435"等于"1079654173767686669"', function () {
-    expect(add('843529812342341234', '236124361425345435')).toBe('1079654173767686669')
+    expect(add('843529812342341234', '236124361425345435')).toBe(
+      '1079654173767686669'
+    )
   })
-})
\ No newline at end of file
+})