diff --git a/.gitignore b/.gitignore
index f81c85dc..7f5f6761 100644
--- a/.gitignore
+++ b/.gitignore
@@ -32,6 +32,8 @@ rustlib/pkg/
 .coverage
 .coverage.*
 coverage.xml
+tslib/storage/test/asset/*.log
+tslib/storage/test/asset/*.db
 
 # Others
 .envrc
diff --git a/tslib/storage/package.json b/tslib/storage/package.json
index 0a1749cc..bc2c5707 100644
--- a/tslib/storage/package.json
+++ b/tslib/storage/package.json
@@ -1,5 +1,6 @@
 {
   "name": "@optuna/storage",
+  "type": "module",
   "private": true,
   "version": "0.0.1",
   "description": "Loaders for Optuna storages",
diff --git a/tslib/storage/test/asset/generate_test_asset.py b/tslib/storage/test/asset/generate_test_asset.py
new file mode 100644
index 00000000..e17d92fe
--- /dev/null
+++ b/tslib/storage/test/asset/generate_test_asset.py
@@ -0,0 +1,17 @@
+import os.path
+import optuna
+
+
+BASE_DIR = os.path.dirname(os.path.abspath(__file__))
+
+
+def objective(trial):
+    x = trial.suggest_uniform('x', -10, 10)
+    return (x - 2) ** 2
+
+
+if __name__ == '__main__':
+    journal_backend = optuna.storages.JournalFileStorage(os.path.join(BASE_DIR, "journal.log"))
+    storage = optuna.storages.JournalStorage(journal_backend)
+    study = optuna.create_study(storage=storage)
+    study.optimize(objective, n_trials=100)
diff --git a/tslib/storage/test/journal.test.mjs b/tslib/storage/test/journal.test.mjs
new file mode 100644
index 00000000..9f140b9f
--- /dev/null
+++ b/tslib/storage/test/journal.test.mjs
@@ -0,0 +1,15 @@
+import test from "node:test";
+import assert from "node:assert";
+import path from "node:path";
+import { openAsBlob } from "node:fs";
+
+import * as mut from "../pkg/journal.js";
+
+test("Test Journal File Storage", async () => {
+    const blob = await openAsBlob(path.resolve(".", "test", "asset", "journal.log"));
+    const buf = await blob.arrayBuffer();
+    const storage = new mut.JournalFileStorage(buf);
+    const studies = await storage.getStudies();
+
+    assert.strictEqual(studies.length, 1);
+});
diff --git a/tslib/storage/tsconfig.json b/tslib/storage/tsconfig.json
index 67b2c70d..0a5c296b 100644
--- a/tslib/storage/tsconfig.json
+++ b/tslib/storage/tsconfig.json
@@ -14,7 +14,7 @@
         "rootDir": "./src",
         "outDir": "./pkg",
         "allowSyntheticDefaultImports": true,
-        "target": "es5",
+        "target": "es2021",
         "sourceMap": true,
         "declaration": true,
         "strict": true