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// Copyright 2013 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
function focus(element) {
// Focus the target element in order to send keys to it.
// First, the currently active element is blurred, if it is different from
// the target element. We do not want to blur an element unnecessarily,
// because this may cause us to lose the current cursor position in the
// element.
// Secondly, we focus the target element.
// Thirdly, we check if the new active element is the target element. If not,
// we throw an error.
// Additional notes:
// - |document.activeElement| is the currently focused element, or body if
// no element is focused
// - Even if |document.hasFocus()| returns true and the active element is
// the body, sometimes we still need to focus the body element for send
// keys to work. Not sure why
// - You cannot focus a descendant of a content editable node
// - V8 throws a TypeError when calling setSelectionRange for a non-text
// input, which still have setSelectionRange defined. For chrome 29+, V8
// throws a DOMException with code InvalidStateError.
var doc = element.ownerDocument || element;
var prevActiveElement = doc.activeElement;
if (element != prevActiveElement && prevActiveElement)
prevActiveElement.blur();
element.focus();
var activeElement = doc.activeElement;
// If the element is in a shadow DOM, then as far as the document is
// concerned, the shadow host is the active element. We need to go through the
// tree of shadow DOMs to check that the element we gave focus to is now
// active.
if (element != activeElement && !element.contains(activeElement)) {
var shadowRoot = activeElement.shadowRoot;
while (shadowRoot) {
var activeElement = shadowRoot.activeElement;
if (element == activeElement) {
// the shadow DOM's active element is our requested element. We're good.
break;
}
// The shadow DOM's active element isn't our requested element, check to
// see if there's a nested shadow DOM.
shadowRoot = activeElement.shadowRoot;
}
}
if (element != activeElement && !element.contains(activeElement))
throw new Error('cannot focus element');
}
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