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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
"use strict";
/**
* Scroll the document so that the element "elem" appears in the viewport.
*
* @param {DOMNode} elem
* The element that needs to appear in the viewport.
* @param {Boolean} centered
* true if you want it centered, false if you want it to appear on the
* top of the viewport. It is true by default, and that is usually what
* you want.
*/
function scrollIntoViewIfNeeded(elem, centered = true) {
let win = elem.ownerDocument.defaultView;
let clientRect = elem.getBoundingClientRect();
// The following are always from the {top, bottom}
// of the viewport, to the {top, …} of the box.
// Think of them as geometrical vectors, it helps.
// The origin is at the top left.
let topToBottom = clientRect.bottom;
let bottomToTop = clientRect.top - win.innerHeight;
// We allow one translation on the y axis.
let yAllowed = true;
// Whatever `centered` is, the behavior is the same if the box is
// (even partially) visible.
if ((topToBottom > 0 || !centered) && topToBottom <= elem.offsetHeight) {
win.scrollBy(0, topToBottom - elem.offsetHeight);
yAllowed = false;
} else if ((bottomToTop < 0 || !centered) &&
bottomToTop >= -elem.offsetHeight) {
win.scrollBy(0, bottomToTop + elem.offsetHeight);
yAllowed = false;
}
// If we want it centered, and the box is completely hidden,
// then we center it explicitly.
if (centered) {
if (yAllowed && (topToBottom <= 0 || bottomToTop >= 0)) {
win.scroll(win.scrollX,
win.scrollY + clientRect.top
- (win.innerHeight - elem.offsetHeight) / 2);
}
}
}
exports.scrollIntoViewIfNeeded = scrollIntoViewIfNeeded;
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