1// Copyright (c) 2013 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5function focus(element) {
6  // Focus the target element in order to send keys to it.
7  // First, the currently active element is blurred, if it is different from
8  // the target element. We do not want to blur an element unnecessarily,
9  // because this may cause us to lose the current cursor position in the
10  // element.
11  // Secondly, we focus the target element.
12  // Thirdly, if the target element is newly focused and is a text input, we
13  // set the cursor position at the end.
14  // Fourthly, we check if the new active element is the target element. If not,
15  // we throw an error.
16  // Additional notes:
17  //   - |document.activeElement| is the currently focused element, or body if
18  //     no element is focused
19  //   - Even if |document.hasFocus()| returns true and the active element is
20  //     the body, sometimes we still need to focus the body element for send
21  //     keys to work. Not sure why
22  //   - You cannot focus a descendant of a content editable node
23  //   - V8 throws a TypeError when calling setSelectionRange for a non-text
24  //     input, which still have setSelectionRange defined. For chrome 29+, V8
25  //     throws a DOMException with code InvalidStateError.
26  var doc = element.ownerDocument || element;
27  var prevActiveElement = doc.activeElement;
28  if (element != prevActiveElement && prevActiveElement)
29    prevActiveElement.blur();
30  element.focus();
31  if (element != prevActiveElement && element.value &&
32      element.value.length && element.setSelectionRange) {
33    try {
34      element.setSelectionRange(element.value.length, element.value.length);
35    } catch (error) {
36      if (!(error instanceof TypeError) && !(error instanceof DOMException &&
37          error.code == DOMException.INVALID_STATE_ERR))
38        throw error;
39    }
40  }
41  if (element != doc.activeElement)
42    throw new Error('cannot focus element');
43}
44