Add client-side connection sanity check before firing a send message

.dynamic/client/patron.js

@@ -3,8 +3,6 @@ window.addEventListener('load', _ => {
   $ = document.querySelector.bind(document)
   const Modal = Swal
 
-
-
   const socket = new WebSocket(`wss://${window.location.hostname}/patron`)
 
   // Handle connectivity.
@@ -120,6 +118,13 @@ window.addEventListener('load', _ => {
         itemId
       }
 
+      // Sanity check: socket must be open.
+      // (Note: our validation should have caught this by this stage and it’s a bug if it hasn’t.)
+      if (socket.readyState !== WebSocket.OPEN) {
+        Modal.fire('Not connected', `Sorry, we cannot ${command.action} your patronage right now as we cannot connect to the server.`, 'error')
+        return
+      }
+
       if (commandName === 'update') {
         command.amount = $('#patronageAmount').value
         $('#update-button').value = 'Updating…'
@@ -145,7 +150,12 @@ window.addEventListener('load', _ => {
         $('#cancel-button').value = 'Cancelling…'
       }
 
-      socket.send(JSON.stringify(command))
+      try {
+        socket.send(JSON.stringify(command))
+      } catch (error) {
+        console.log('Cannot send message', error)
+        Modal.fire('Cannot send message', error, 'error')
+      }
     })
   }