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