Handle non-insert changes

backend/server.js

@@ -33,7 +33,6 @@ async function run() {
   console.log("Started watching changes in database");
 
   const writeMessage = (response, blob) => {
-    // TODO: why no id?
     const id = blob._id || null
     const message = `id: ${id}\nevent: message\ndata: ${JSON.stringify(blob)}\n\n`
     response.write(message)
@@ -55,8 +54,11 @@ async function run() {
         });
 
     const changeListener = async (change) => {
+      // Ignore events without fullDocument, e.g. deletes.
+      if (change.fullDocument) {
         writeMessage(response, change.fullDocument)
       }
+    }
     changeStream.on("change", changeListener);
     response.on('close', () => {
       changeStream.removeListener("change", changeListener)