Add colin's versions of nextTab.

addon/main.coffee

@@ -7,6 +7,49 @@ handleBrowserAction = () ->
     # example of a named function, but anonymous functions are fine, too.
     browser.tabs.query({active: true}).then(console.log)
 
+# Change to the next tab in window, wrapping back to the start, if req.
+#
+# Get an array of all tabs, find the active tab's index, and the tab id of
+# the tab with the next index.
+#
+# TODO: limit to focused window.
+nextTab1 = () ->
+    browser.tabs.query({}).then(
+        (tabs) ->
+            # Doing my own list comprehensions means they're not done
+            # asynchronously from each other, but they will be very fast and
+            # this makes the code much simpler.
+            active = (tab for tab in tabs when tab.active == true)[0]
+            target_index = (active.index + 1) % tabs.length
+            target = (tab for tab in tabs when tab.index == target_index)[0]
+            displayTab(target.id)
+        , console.error)
+
+# Change to the next tab in window, wrapping back to the start, if req.
+#
+# Get an array of all tabs, find the active tab's index, and the tab id of
+# the tab with the next index.
+#
+# TODO: limit to focused window.
+nextTab2 = () ->
+    # Alternative implementation without list comprehensions.
+    browser.tabs.query({}).then(
+        (tabs) ->
+            browser.tabs.query({active: true}).then(
+                (tabs2) ->
+                    active = tabs2[0]
+                    target_index = (active.index + 1) % tabs.length
+                    browser.tabs.query({index: target_index}).then(
+                        (tabs3) ->
+                            displayTab(tabs3[0].id)
+                    , console.error)
+            , console.error)
+    , console.error)
+
+# Convenience: mark tab_id as active (active tabs are displayed in their window)
+displayTab = (tab_id) ->
+    browser.tabs.update(tab_id, {active: true}).then(null, console.error)
+
 # Example of a listener. Presumably we wouldn't use the browserAction button in
 # the real thing.
 browser.browserAction.onClicked.addListener(handleBrowserAction)