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/*
* Copyright 2020 Adobe. All rights reserved.
* This file is licensed to you under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License. You may obtain a copy
* of the License at http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software distributed under
* the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR REPRESENTATIONS
* OF ANY KIND, either express or implied. See the License for the specific language
* governing permissions and limitations under the License.
*/
/**
* Scrolls `scrollView` so that `element` is visible.
* Similar to `element.scrollIntoView({block: 'nearest'})` (not supported in Edge),
* but doesn't affect parents above `scrollView`.
*/
export function scrollIntoView(scrollView: HTMLElement, element: HTMLElement) {
let offsetX = relativeOffset(scrollView, element, 'left');
let offsetY = relativeOffset(scrollView, element, 'top');
let width = element.offsetWidth;
let height = element.offsetHeight;
let x = scrollView.scrollLeft;
let y = scrollView.scrollTop;
let maxX = x + scrollView.offsetWidth;
let maxY = y + scrollView.offsetHeight;
if (offsetX <= x) {
x = offsetX;
} else if (offsetX + width > maxX) {
x += offsetX + width - maxX;
}
if (offsetY <= y) {
y = offsetY;
} else if (offsetY + height > maxY) {
y += offsetY + height - maxY;
}
scrollView.scrollLeft = x;
scrollView.scrollTop = y;
}
/**
* Computes the offset left or top from child to ancestor by accumulating
* offsetLeft or offsetTop through intervening offsetParents.
*/
function relativeOffset(ancestor: HTMLElement, child: HTMLElement, axis: 'left'|'top') {
const prop = axis === 'left' ? 'offsetLeft' : 'offsetTop';
let sum = 0;
while (child.offsetParent) {
sum += child[prop];
if (child.offsetParent === ancestor) {
// Stop once we have found the ancestor we are interested in.
break;
} else if (child.offsetParent.contains(ancestor)) {
// If the ancestor is not `position:relative`, then we stop at
// _its_ offset parent, and we subtract off _its_ offset, so that
// we end up with the proper offset from child to ancestor.
sum -= ancestor[prop];
break;
}
child = child.offsetParent as HTMLElement;
}
return sum;
}