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Clean-up variable definitions in getVisibleElements

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With modern JavaScript supporting block-scoped variables, it's no longer necessary to have large numbers of top-level variable definitions (especially when all variables are, implicitly, set to `undefined`).

Besides moving variable definintions, a number of them are also converted to `const` to help ensure that they cannot be *accidentally* modified in the code.
Finally, the `views.length` calculation is now cached *once* rather than being re-computed multiple times.
This commit is contained in:
Jonas Jenwald 2019-01-11 13:18:36 +01:00
parent 35415b935c
commit ae59be181b
1 changed files with 24 additions and 31 deletions
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55
web/ui_utils.js
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@ -413,8 +413,8 @@ function backtrackBeforeAllVisibleElements(index, views, top) {
*/ */
function getVisibleElements(scrollEl, views, sortByVisibility = false, function getVisibleElements(scrollEl, views, sortByVisibility = false,
horizontal = false) { horizontal = false) {
let top = scrollEl.scrollTop, bottom = top + scrollEl.clientHeight; const top = scrollEl.scrollTop, bottom = top + scrollEl.clientHeight;
let left = scrollEl.scrollLeft, right = left + scrollEl.clientWidth; const left = scrollEl.scrollLeft, right = left + scrollEl.clientWidth;
// Throughout this "generic" function, comments will assume we're working with // Throughout this "generic" function, comments will assume we're working with
// PDF document pages, which is the most important and complex case. In this // PDF document pages, which is the most important and complex case. In this
@ -427,27 +427,24 @@ function getVisibleElements(scrollEl, views, sortByVisibility = false,
// the border). Adding clientWidth/Height gets us the bottom-right corner of // the border). Adding clientWidth/Height gets us the bottom-right corner of
// the padding edge. // the padding edge.
function isElementBottomAfterViewTop(view) { function isElementBottomAfterViewTop(view) {
let element = view.div; const element = view.div;
let elementBottom = const elementBottom =
element.offsetTop + element.clientTop + element.clientHeight; element.offsetTop + element.clientTop + element.clientHeight;
return elementBottom > top; return elementBottom > top;
} }
function isElementRightAfterViewLeft(view) { function isElementRightAfterViewLeft(view) {
let element = view.div; const element = view.div;
let elementRight = const elementRight =
element.offsetLeft + element.clientLeft + element.clientWidth; element.offsetLeft + element.clientLeft + element.clientWidth;
return elementRight > left; return elementRight > left;
} }
let visible = [], view, element; const visible = [], numViews = views.length;
let currentHeight, viewHeight, viewBottom, hiddenHeight; let firstVisibleElementInd = numViews === 0 ? 0 :
let currentWidth, viewWidth, viewRight, hiddenWidth;
let percentVisible;
let firstVisibleElementInd = views.length === 0 ? 0 :
binarySearchFirstItem(views, horizontal ? isElementRightAfterViewLeft : binarySearchFirstItem(views, horizontal ? isElementRightAfterViewLeft :
isElementBottomAfterViewTop); isElementBottomAfterViewTop);
if (views.length > 0 && !horizontal) { if (numViews > 0 && !horizontal) {
// In wrapped scrolling (or vertical scrolling with spreads), with some page // In wrapped scrolling (or vertical scrolling with spreads), with some page
// sizes, isElementBottomAfterViewTop doesn't satisfy the binary search // sizes, isElementBottomAfterViewTop doesn't satisfy the binary search
// condition: there can be pages with bottoms above the view top between // condition: there can be pages with bottoms above the view top between
@ -467,15 +464,13 @@ function getVisibleElements(scrollEl, views, sortByVisibility = false,
// we pass `right`, without needing the code below that handles the -1 case. // we pass `right`, without needing the code below that handles the -1 case.
let lastEdge = horizontal ? right : -1; let lastEdge = horizontal ? right : -1;
for (let i = firstVisibleElementInd, ii = views.length; i < ii; i++) { for (let i = firstVisibleElementInd; i < numViews; i++) {
view = views[i]; const view = views[i], element = view.div;
element = view.div; const currentWidth = element.offsetLeft + element.clientLeft;
currentWidth = element.offsetLeft + element.clientLeft; const currentHeight = element.offsetTop + element.clientTop;
currentHeight = element.offsetTop + element.clientTop; const viewWidth = element.clientWidth, viewHeight = element.clientHeight;
viewWidth = element.clientWidth; const viewRight = currentWidth + viewWidth;
viewHeight = element.clientHeight; const viewBottom = currentHeight + viewHeight;
viewRight = currentWidth + viewWidth;
viewBottom = currentHeight + viewHeight;
if (lastEdge === -1) { if (lastEdge === -1) {
// As commented above, this is only needed in non-horizontal cases. // As commented above, this is only needed in non-horizontal cases.
@ -494,24 +489,22 @@ function getVisibleElements(scrollEl, views, sortByVisibility = false,
continue; continue;
} }
hiddenHeight = Math.max(0, top - currentHeight) + const hiddenHeight = Math.max(0, top - currentHeight) +
Math.max(0, viewBottom - bottom); Math.max(0, viewBottom - bottom);
hiddenWidth = Math.max(0, left - currentWidth) + const hiddenWidth = Math.max(0, left - currentWidth) +
Math.max(0, viewRight - right); Math.max(0, viewRight - right);
percentVisible = ((viewHeight - hiddenHeight) * (viewWidth - hiddenWidth) * const percent = ((viewHeight - hiddenHeight) * (viewWidth - hiddenWidth) *
100 / viewHeight / viewWidth) | 0; 100 / viewHeight / viewWidth) | 0;
visible.push({ visible.push({
id: view.id, id: view.id,
x: currentWidth, x: currentWidth,
y: currentHeight, y: currentHeight,
view, view,
percent: percentVisible, percent,
}); });
} }
let first = visible[0]; const first = visible[0], last = visible[visible.length - 1];
let last = visible[visible.length - 1];
if (sortByVisibility) { if (sortByVisibility) {
visible.sort(function(a, b) { visible.sort(function(a, b) {