created functions retrieving all topics

functions/handlers/topic.js

@@ -0,0 +1,35 @@
+/* eslint-disable promise/always-return */
+const admin = require('firebase-admin');
+exports.putTopic = (req, res) => {
+
+    const newTopic = {
+        topic: req.body.topic
+    };
+
+    admin.firestore().collection('topics').add(newTopic)
+    .then((doc) => {
+        const resTopic = newTopic;
+        return res.status(200).json(resTopic);
+    })
+    .catch((err) => {
+        console.error(err);
+        return res.status(500).json({ error: 'something is wrong'});
+    });
+};
+
+
+
+exports.getAllTopics = (req, res) => {
+    admin.firestore().collection('topics').get()
+    .then((data) => {
+        let topics = [];
+        data.forEach(function(doc) {
+            topics.push(doc.data());
+        });
+        return res.status(200).json(topics);
+    })
+    .catch((err) => {
+        console.error(err);
+        return res.status(500).json({error: 'Failed to fetch all posts written by specific user.'})
+    })
+};