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Change the getVisibleElements helper function to take a parameter object

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Given the number of parameters, and the fact that many of them are booleans, the call-sites are no longer particularly easy to read and understand. Furthermore, this slightly improves the formatting of the JSDoc-comment, since it needed updating as part of these changes anyway.

Finally, this removes an unnecessary `numViews === 0` check from `getVisibleElements`, since that should be *very* rare and more importantly that the `binarySearchFirstItem` function already has a fast-path for that particular case.
This commit is contained in:
Jonas Jenwald 2020-11-04 12:05:29 +01:00
parent 4e13559cb0
commit ba761e42f0
4 changed files with 55 additions and 41 deletions
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45
web/ui_utils.js
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@ -411,6 +411,21 @@ function backtrackBeforeAllVisibleElements(index, views, top) {
return index;
}
/**
* @typedef {Object} GetVisibleElementsParameters
* @property {HTMLElement} scrollEl - A container that can possibly scroll.
* @property {Array} views - Objects with a `div` property that contains an
* HTMLElement, which should all be descendants of `scrollEl` satisfying the
* relevant layout assumptions.
* @property {boolean} sortByVisibility - If `true`, the returned elements are
* sorted in descending order of the percent of their padding box that is
* visible. The default value is `false`.
* @property {boolean} horizontal - If `true`, the elements are assumed to be
* laid out horizontally instead of vertically. The default value is `false`.
* @property {boolean} rtl - If `true`, the `scrollEl` container is assumed to
* be in right-to-left mode. The default value is `false`.
*/
/**
* Generic helper to find out what elements are visible within a scroll pane.
*
@ -428,23 +443,16 @@ function backtrackBeforeAllVisibleElements(index, views, top) {
* rendering canvas. Earlier and later refer to index in `views`, not page
* layout.)
*
* @param scrollEl {HTMLElement} - a container that can possibly scroll
* @param views {Array} - objects with a `div` property that contains an
* HTMLElement, which should all be descendents of `scrollEl` satisfying the
* above layout assumptions
* @param sortByVisibility {boolean} - if true, the returned elements are sorted
* in descending order of the percent of their padding box that is visible
* @param horizontal {boolean} - if true, the elements are assumed to be laid
* out horizontally instead of vertically
* @param {GetVisibleElementsParameters}
* @returns {Object} `{ first, last, views: [{ id, x, y, view, percent }] }`
*/
function getVisibleElements(
function getVisibleElements({
scrollEl,
views,
sortByVisibility = false,
horizontal = false,
rtl = false
) {
rtl = false,
}) {
const top = scrollEl.scrollTop,
bottom = top + scrollEl.clientHeight;
const left = scrollEl.scrollLeft,
@ -475,15 +483,12 @@ function getVisibleElements(
const visible = [],
numViews = views.length;
let firstVisibleElementInd =
numViews === 0
? 0
: binarySearchFirstItem(
views,
horizontal
? isElementNextAfterViewHorizontally
: isElementBottomAfterViewTop
);
let firstVisibleElementInd = binarySearchFirstItem(
views,
horizontal
? isElementNextAfterViewHorizontally
: isElementBottomAfterViewTop
);
// Please note the return value of the `binarySearchFirstItem` function when
// no valid element is found (hence the `firstVisibleElementInd` check below).