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# Copyright 2016 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
from telemetry.internal.actions import page_action
from telemetry.internal.actions.scroll import ScrollAction
from telemetry.util import js_template
class ScrollToElementAction(page_action.PageAction):
def __init__(self, selector=None, element_function=None,
container_selector=None, container_element_function=None,
"""Perform scroll gesture on container until an element is in view.
Both the element and the container can be specified by a CSS selector
xor a JavaScript function, provided as a string, which returns an element.
The element is required so exactly one of selector and element_function
must be provided. The container is optional so at most one of
container_selector and container_element_function can be provided.
The container defaults to document.scrollingElement or document.body if
scrollingElement is not set.
selector: A CSS selector describing the element.
element_function: A JavaScript function (as string) that is used
to retrieve the element. For example:
'function() { return foo.element; }'.
container_selector: A CSS selector describing the container element.
container_element_function: A JavaScript function (as a string) that is
used to retrieve the container element.
speed_in_pixels_per_second: Speed to scroll.
super(ScrollToElementAction, self).__init__()
self._selector = selector
self._element_function = element_function
self._container_selector = container_selector
self._container_element_function = container_element_function
self._speed = speed_in_pixels_per_second
self._distance = None
self._direction = None
self._scroller = None
assert (self._selector or self._element_function), (
'Must have either selector or element function')
def WillRunAction(self, tab):
if self._selector:
element = js_template.Render(
'document.querySelector({{ selector }})', selector=self._selector)
element = self._element_function
self._distance = tab.EvaluateJavaScript('''
var rect = elem.getBoundingClientRect();
if (rect.bottom < 0) {
// The bottom of the element is above the viewport.
// Scroll up until the top of the element is on screen.
return - (window.innerHeight / 2);
if ( - window.innerHeight >= 0) {
// provides the pixel offset of the element from the
// top of the page. Because that exceeds the viewport's height,
// we know that the element is below the viewport.
return - (window.innerHeight / 2);
return 0;
})({{ @element }});
''', element=element)
self._direction = 'down' if self._distance > 0 else 'up'
self._distance = abs(self._distance)
self._scroller = ScrollAction(
def RunAction(self, tab):
if self._distance == 0: # Element is already in view.