composebox_typeahead: Extract autocomplete_checks.

static/js/composebox_typeahead.js

@@ -174,6 +174,23 @@ function select_on_focus(field_id) {
     });
 }
 
+function autocomplete_checks(q, char) {
+    // Don't autocomplete more than this many characters.
+    var max_chars = 30;
+    var last_at = q.lastIndexOf(char);
+    if (last_at === -1 || last_at < q.length-1 - max_chars) {
+        return false;  // char doesn't appear, or too far back
+    }
+
+    // Only match if the char follows a space, various punctuation,
+    // or is at the beginning of the string.
+    if (last_at > 0 && "\n\t \"'(){}[]".indexOf(q[last_at-1]) === -1) {
+        return false;
+    }
+
+    return true;
+}
+
 exports.split_at_cursor = function (query, input) {
     var cursor = input.caret();
     return [query.slice(0, cursor), query.slice(cursor)];
@@ -207,19 +224,11 @@ exports.compose_content_begins_typeahead = function (query) {
         return false;
     }
 
-    // Don't autocomplete more than this many characters.
+    if (!autocomplete_checks(q, '@')) {
-    var max_chars = 30;
-    var last_at = q.lastIndexOf('@');
-    if (last_at === -1 || last_at < q.length-1 - max_chars) {
-        return false;  // No '@', or too far back
-    }
-
-    // Only match if the @ follows a space, various punctuation,
-    // or is at the beginning of the string.
-    if (last_at > 0 && "\n\t \"'(){}[]".indexOf(q[last_at-1]) === -1) {
         return false;
     }
 
+    var last_at = q.lastIndexOf('@');
     current_token = q.substring(last_at + 1);
     if (current_token.length < 1 || current_token.lastIndexOf('*') !== -1) {
         return false;