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chore: Remove redundant JS in index.html when no feature flags are enabled #24212

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chore: Remove redundant JS in index.html when no feature flags are enabled #24212

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e550220
Initial plan
Codex Apr 28, 2026
e1179a4
Fix: omit feature flags JS when none enabled
Apr 28, 2026
c881ae3
test: adjust feature flags expectations
Codex Apr 28, 2026
d41000d
Addressing PR comments
Codex Apr 28, 2026
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25 changes: 16 additions & 9 deletions flow-server/src/main/java/com/vaadin/flow/server/communication/IndexHtmlRequestHandler.java
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Original file line number Diff line number Diff line change
Expand Up @@ -219,23 +219,30 @@ public boolean synchronizedHandleRequest(VaadinSession session,
private void initializeFeatureFlags(Document indexDocument,
VaadinRequest request) {
String script = featureFlagsInitializer(request);
if (script.isEmpty()) {
return;
}
Element scriptElement = indexDocument.head().prependElement("script");
scriptElement.attr(SCRIPT_INITIAL, "");
scriptElement.appendChild(new DataNode(script));
}

static String featureFlagsInitializer(VaadinRequest request) {
return FeatureFlags.get(request.getService().getContext()).getFeatures()
.stream().filter(Feature::isEnabled)
String activations = FeatureFlags.get(request.getService().getContext())
.getFeatures().stream().filter(Feature::isEnabled)
.map(feature -> String.format("activator(\"%s\");",
feature.getId()))
.collect(Collectors.joining("\n",
"""
window.Vaadin = window.Vaadin || {};
window.Vaadin.featureFlagsUpdaters = window.Vaadin.featureFlagsUpdaters || [];
window.Vaadin.featureFlagsUpdaters.push((activator) => {
""",
"});"));
.collect(Collectors.joining("\n"));

if (activations.isEmpty()) {
return "";
}

return """
window.Vaadin = window.Vaadin || {};
window.Vaadin.featureFlagsUpdaters = window.Vaadin.featureFlagsUpdaters || [];
window.Vaadin.featureFlagsUpdaters.push((activator) => {
""" + activations + "\n});";
}

private static void addDevBundleTheme(Document document,
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4 changes: 2 additions & 2 deletions ...erver/src/test/java/com/vaadin/flow/server/communication/IndexHtmlRequestHandlerTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -218,9 +218,9 @@ public void serveIndexHtml_featureFlagsSetter_isPresent()
indexHtmlRequestHandler.synchronizedHandleRequest(session,
createVaadinRequest("/"), response);
String indexHtml = responseOutput.toString(StandardCharsets.UTF_8);
assertTrue(indexHtml.contains(
assertFalse(indexHtml.contains(
"window.Vaadin.featureFlagsUpdaters.push((activator) => {"),
"Response should have Feature Flags updater function");
"Response should not have Feature Flags updater function when no flags are enabled");
}

@Test
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