compose_state.js: Extract focus_in_empty_compose().

Wrote some tests for the function also.

frontend_tests/node_tests/compose_actions.js

@@ -1,5 +1,6 @@
 var noop = function () {};
 var return_false = function () { return false; };
+var return_true = function () { return true; };
 
 set_global('document', {
     location: {
@@ -215,3 +216,24 @@ function assert_hidden(sel) {
                                            trigger: 'new topic button'}),
                  'subject');
 }());
+
+(function test_focus_in_empty_compose() {
+    $('#new_message_content').is = function (attr) {
+        assert.equal(attr, ':focus');
+        return $('#new_message_content').is_focused;
+    };
+
+    compose_state.composing = return_true;
+    $('#new_message_content').val('');
+    $('#new_message_content').focus();
+    assert(compose_state.focus_in_empty_compose());
+
+    compose_state.composing = return_false;
+    assert(!compose_state.focus_in_empty_compose());
+
+    $('#new_message_content').val('foo');
+    assert(!compose_state.focus_in_empty_compose());
+
+    $('#new_message_content').blur();
+    assert(!compose_state.focus_in_empty_compose());
+}());

static/js/compose_state.js

@@ -18,6 +18,13 @@ exports.composing = function () {
     return !!message_type;
 };
 
+exports.focus_in_empty_compose = function () {
+    return (
+        exports.composing() &&
+        exports.message_content() === "" &&
+        $('#new_message_content').is(':focus'));
+};
+
 function get_or_set(fieldname, keep_leading_whitespace) {
     // We can't hoist the assignment of 'elem' out of this lambda,
     // because the DOM element might not exist yet when get_or_set

static/js/hotkey.js

@@ -7,14 +7,6 @@ function do_narrow_action(action) {
     return true;
 }
 
-
-function focus_in_empty_compose() {
-    return (
-        compose_state.composing() &&
-        compose_state.message_content() === "" &&
-        $('#new_message_content').is(':focus'));
-}
-
 function open_reactions() {
     var message = current_msg_list.selected_message();
     var target = $(current_msg_list.selected_row()).find(".actions_hover")[0];
@@ -522,12 +514,12 @@ exports.process_hotkey = function (e, hotkey) {
         // Note that there is special handling for enter/escape too, but
         // we handle this in other functions.
 
-        if (event_name === 'left_arrow' && focus_in_empty_compose()) {
+        if (event_name === 'left_arrow' && compose_state.focus_in_empty_compose()) {
             message_edit.edit_last_sent_message();
             return true;
         }
 
-        if ((event_name === 'up_arrow' || event_name === 'down_arrow') && focus_in_empty_compose()) {
+        if ((event_name === 'up_arrow' || event_name === 'down_arrow') && compose_state.focus_in_empty_compose()) {
             compose_actions.cancel();
             // don't return, as we still want it to be picked up by the code below
         } else if (event_name === "page_up") {