This combination of JS things works.

resources/js/components/InfoBox.react.js

@@ -0,0 +1,50 @@
+/*
+ * InfoBox.react.js
+ * Copyright (c) 2019 thegrumpydictator@gmail.com
+ *
+ * This file is part of Firefly III.
+ *
+ * Firefly III is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Firefly III is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Firefly III. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+import React from 'react';
+import axios from 'axios';
+
+class InfoBox extends React.Component {
+    state = {
+        posts: []
+    };
+
+    componentDidMount() {
+        axios.get(`http://www.reddit.com/r/${this.props.subreddit}.json`)
+            .then(res => {
+                const posts = res.data.data.children.map(obj => obj.data);
+                this.setState({ posts });
+            });
+    }
+
+    render() {
+        return (
+            <div>
+                <h1>{`/r/${this.props.subreddit}`}</h1>
+                <ul>
+                    {this.state.posts.map(post =>
+                                              <li key={post.id}>{post.title}</li>
+                    )}
+                </ul>
+            </div>
+        );
+    }
+}
+export default InfoBox;