implement simple tab switch

src/background/index.js

@@ -1,4 +1,18 @@
+import * as tabs from './tabs';
+
+const KEY_MAP = {
+  'tabs.prev': 104,
+  'tabs.next': 108
+};
+
 browser.runtime.onMessage.addListener((request, sender, sendResponse) => {
-  console.log("Pressed " + request.which);
-  sendResponse({ response: "Response from background script" });
+  switch (request.key) {
+  case KEY_MAP['tabs.prev']:
+    tabs.selectPrevTab(sender.tab.index);
+    break;
+  case KEY_MAP['tabs.next']:
+    tabs.selectNextTab(sender.tab.index);
+    break;
+  }
+  sendResponse();
 });

src/background/tabs.js

@@ -0,0 +1,23 @@
+const selectPrevTab = (current) => {
+  chrome.tabs.query({ currentWindow: true }, (tabs) => {
+    if (tabs.length < 2) {
+      return;
+    }
+    let select = (current - 1) % tabs.length
+    let id = tabs[select].id;
+    chrome.tabs.update(id, { active: true })
+  });
+};
+
+const selectNextTab = (current) => {
+  chrome.tabs.query({ currentWindow: true }, (tabs) => {
+    if (tabs.length < 2) {
+      return;
+    }
+    let select = (current + 1 + tabs.length) % tabs.length
+    let id = tabs[select].id;
+    chrome.tabs.update(id, { active: true })
+  });
+};
+
+export { selectNextTab, selectPrevTab };