making it work.

extension/options.js

@@ -2,14 +2,26 @@
 
 import browser from 'webextension-polyfill'
 
-document.getElementById('privateKeyInput').addEventListener('input', ev => {
-  browser.storage.local
-    .set({private_key: document.getElementById('privateKeyInput').value})
-    .then(() => {
-      console.log('success')
-    })
-})
+document
+  .getElementById('privateKeyInput')
+  .addEventListener('input', async ev => {
+    try {
+      await browser.storage.local.set({
+        private_key: document.getElementById('privateKeyInput').value
+      })
+      showMessage('saved!')
+    } catch (err) {
+      showMessage(`error! ${err}`)
+    }
+  })
 
 browser.storage.local.get('private_key').then(results => {
   document.getElementById('privateKeyInput').value = results.private_key
 })
+
+function showMessage(str) {
+  document.getElementById('message').innerHTML = str
+  setTimeout(() => {
+    document.getElementById('message').innerHTML = ''
+  }, 5000)
+}