From 7e1ba3ff90e870e39157f4297ee2be385bd9576b Mon Sep 17 00:00:00 2001
From: Sangwan Jeon <maxswjeon@codingbear.kr>
Date: Sun, 16 Apr 2023 00:21:59 +0900
Subject: [PATCH] fix: bug on append

---
 package.json        |  2 +-
 src/Flat.ts         | 11 +++++++++++
 test/append.test.ts | 16 ++++++++++++++++
 3 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/package.json b/package.json
index 84d232c..01920b5 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "flattype",
-  "version": "0.3.0",
+  "version": "0.3.1",
   "description": "A simple library for creating flat types",
   "main": "dist/Flat.js",
   "module": "dist/Flat.js",
diff --git a/src/Flat.ts b/src/Flat.ts
index ce004b7..60647af 100644
--- a/src/Flat.ts
+++ b/src/Flat.ts
@@ -279,6 +279,17 @@ export default class Flat {
       throw new Error("Flat is not an array");
     }
 
+    const subKeys = Object.keys(this.flat).filter(
+      (flatKey) => flatKey.startsWith(key) && flatKey !== key
+    );
+
+    if (subKeys.length === 0) {
+      const newKey = key === "" ? "0" : `${key}__0`;
+      this.set(newKey, value);
+
+      return this;
+    }
+
     const index = Object.keys(this.flat).filter(
       (flatKey) =>
         flatKey.startsWith(key) && !flatKey.slice(key.length).includes("__")
diff --git a/test/append.test.ts b/test/append.test.ts
index 68ee5c2..c256f2d 100644
--- a/test/append.test.ts
+++ b/test/append.test.ts
@@ -12,12 +12,28 @@ describe("append(key: string, value: any) function", () => {
     });
   });
 
+  it("should append value by key on empty array", () => {
+    const flat = Flat.from({
+      foo: [],
+    });
+
+    expect(flat.append("foo", "baz").getData()).toEqual({
+      foo: ["baz"],
+    });
+  });
+
   it("should append value by key on root", () => {
     const flat = Flat.from(["foo"]);
 
     expect(flat.append("", "baz").getData()).toEqual(["foo", "baz"]);
   });
 
+  it("should append value by key on root when root is empty array", () => {
+    const flat = Flat.from([]);
+
+    expect(flat.append("", "baz").getData()).toEqual(["baz"]);
+  });
+
   it("should throw an error when tried to append on non existing key", () => {
     const flat = Flat.from({
       foo: "bar",