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[WIP] Remove performance bottleneck in active element preservation #137

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Merged
botandrose merged 2 commits into from
Sep 29, 2025
Merged

[WIP] Remove performance bottleneck in active element preservation #137

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7a912d4
it turns out that Element.contains is really slow, so big perf win by…
botandrose-machine Jul 20, 2025
31ace40
don't bother with active element preservation if the active element i…
botandrose-machine Jul 20, 2025
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23 changes: 22 additions & 1 deletion src/idiomorph.js
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Original file line number Diff line number Diff line change
Expand Up @@ -112,6 +112,7 @@ var Idiomorph = (function () {
* @property {ConfigInternal['callbacks']} callbacks
* @property {ConfigInternal['head']} head
* @property {HTMLDivElement} pantry
* @property {Element[]} activeElementAndParents
*/

//=============================================================================
Expand Down Expand Up @@ -424,7 +425,8 @@ var Idiomorph = (function () {

// if the current node contains active element, stop looking for better future matches,
// because if one is found, this node will be moved to the pantry, reparenting it and thus losing focus
if (cursor.contains(document.activeElement)) break;
// @ts-ignore pretend cursor is Element rather than Node, we're just testing for array inclusion
if (ctx.activeElementAndParents.includes(cursor)) break;

cursor = cursor.nextSibling;
}
Expand Down Expand Up @@ -996,6 +998,7 @@ var Idiomorph = (function () {
idMap: idMap,
persistentIds: persistentIds,
pantry: createPantry(),
activeElementAndParents: createActiveElementAndParents(oldNode),
callbacks: mergedConfig.callbacks,
head: mergedConfig.head,
};
Expand Down Expand Up @@ -1036,6 +1039,24 @@ var Idiomorph = (function () {
return pantry;
}

/**
* @param {Element} oldNode
* @returns {Element[]}
*/
function createActiveElementAndParents(oldNode) {
/** @type {Element[]} */
let activeElementAndParents = [];
let elt = document.activeElement;
if (elt?.tagName !== "BODY" && oldNode.contains(elt)) {
while (elt) {
activeElementAndParents.push(elt);
if (elt === oldNode) break;
elt = elt.parentElement;
}
}
return activeElementAndParents;
}

/**
* Returns all elements with an ID contained within the root element and its descendants
*
Expand Down