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Perf(renderer): Diff attribute writes vs getAttribute [perf-eval] #219

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Perf(renderer): Diff attribute writes vs getAttribute [perf-eval] #219

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Perf(renderer): Diff attribute writes vs getAttribute [perf-eval]
jlukic May 22, 2026
1921c9c
Merge branch 'main' into perf/eval-lever1
jlukic May 22, 2026
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21 changes: 18 additions & 3 deletions packages/renderer/src/engines/native/attribute-binding.js
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Original file line number Diff line number Diff line change
Expand Up @@ -72,19 +72,34 @@ export function bindAttribute({
const isIfDefined = singleEntry?.node.ifDefined || singleEntry?.classification.type === 'boolean';

if (isSingleExpr) {
// This reaction is the sole writer of the attribute, so we shadow the
// last value we wrote and diff in JS rather than reading it back with
// getAttribute (a Blink boundary call) on every re-run. undefined means
// "currently absent" — never written, or cleared by an ifDefined miss.
// The first run always applies, clearing the parsed marker attribute.
let lastWritten;
scope.reaction(element, (comp) => {
const value = singleIsBlock
? renderASTToString([singleEntry.node], data, renderer)
: renderer.lookupExpression(singleEntry.node.value, data);
if (skipFirstWrite && comp.firstRun) { return; }
if (skipFirstWrite && comp.firstRun) {
// Server already rendered the attribute; seed the shadow so the first
// reactive re-run diffs honestly against what's in the DOM.
lastWritten = (isIfDefined && !value) ? undefined : stringifyAttrValue(value);
return;
}

if (isIfDefined && !value) {
element.removeAttribute(attrName);
if (comp.firstRun || lastWritten !== undefined) {
element.removeAttribute(attrName);
lastWritten = undefined;
}
}
else {
const strValue = stringifyAttrValue(value);
if (element.getAttribute(attrName) !== strValue) {
if (comp.firstRun || strValue !== lastWritten) {
element.setAttribute(attrName, strValue);
lastWritten = strValue;
}
}
if (attrName === 'checked' || attrName === 'selected') {
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