diff --git a/258.add-digits.js b/258.add-digits.js
new file mode 100644
index 0000000..1c6e9d7
--- /dev/null
+++ b/258.add-digits.js
@@ -0,0 +1,19 @@
+/**
+ * URL of this problem
+ * https://leetcode.com/problems/add-digits/
+ */
+
+/**
+ * @param {number} num
+ * @return {number}
+ */
+var addDigits = function (num) {
+	let numArr = num.toString().split("");
+
+	while (numArr.length > 1) {
+		const sum = numArr.reduce((a, b) => Number(a) + Number(b), 0);
+		numArr = sum.toString().split("");
+	}
+
+	return Number(numArr[0]);
+};