Demonstrate changing keyboard shortcut values (#347)

* Demonstrate changing keyboard shortcut values

* Add applications key

* Update README

commands/options.js

@@ -0,0 +1,42 @@
+const commandName = 'toggle-feature';
+
+/**
+ * Update the UI: set the value of the shortcut textbox.
+ */
+async function updateUI() {
+  let commands = await browser.commands.getAll();
+  for (command of commands) {
+    if (command.name === commandName) {
+      document.querySelector('#shortcut').value = command.shortcut;
+    }
+  }
+}
+
+/**
+ * Update the shortcut based on the value in the textbox.
+ */
+async function updateShortcut() {
+  await browser.commands.update({
+    name: commandName,
+    shortcut: document.querySelector('#shortcut').value
+  });
+}
+
+/**
+ * Reset the shortcut and update the textbox.
+ */
+async function resetShortcut() {
+  await browser.commands.reset(commandName);
+  updateUI();
+}
+
+/**
+ * Update the UI when the page loads.
+ */
+document.addEventListener('DOMContentLoaded', updateUI);
+
+/**
+ * Handle update and reset button clicks
+ */
+document.querySelector('#update').addEventListener('click', updateShortcut)
+document.querySelector('#reset').addEventListener('click', resetShortcut)