perf(platform-browser): disable styles of removed components instead of removing by mattlewis92 · Pull Request #64524 · angular/angular

mattlewis92 · 2025-10-19T16:47:27Z

This commit changes the behaviour of REMOVE_STYLES_ON_COMPONENT_DESTROY.

Now, style and link nodes are disabled instead of removed from DOM which avoiding the browser having to reparse the stylesheet when the stylesheet is re-enabled.

This was previously reverted in 1640743 but it seems like the observed perf regression in chromium has since been fixed in https://issues.chromium.org/issues/40911913, so it should be possible to reland this perf improvement

PR Checklist

Please check if your PR fulfills the following requirements:

The commit message follows our guidelines: https://github.com/angular/angular/blob/main/contributing-docs/commit-message-guidelines.md
Tests for the changes have been added (for bug fixes / features)
Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

Bugfix
Feature
Code style update (formatting, local variables)
Refactoring (no functional changes, no api changes)
Build related changes
CI related changes
Documentation content changes
angular.dev application / infrastructure changes
Other... Please describe:

What is the current behavior?

When all components using a stylesheet are destroyed, the stylesheet is removed from the DOM

Issue Number: 59651

What is the new behavior?

The stylesheet is now marked as disabled, which improves performance the next time the stylesheet is enabled, as the browser will not have to incur the cost of reparsing the stylesheet when enabling it (although it will still trigger style recalculations)

Does this PR introduce a breaking change?

Yes
No

When a component is destroyed, its associated <style> elements are now
disabled in the DOM rather than removed. When the same component is recreated, the styles
are re-enabled at their original position instead of being re-appended to the end of
<head>. This may change the CSS cascade order of component stylesheets, which could
affect styling if your application relies on the order in which component styles appear
in the DOM.

To migrate, avoid depending on the insertion order of Angular component stylesheets in
<head>. If you have styles that must take precedence over component styles, use more
specific CSS selectors or increase specificity rather than relying on source order.
Applications that do not rely on stylesheet ordering in <head> are not affected.

Other information

alan-agius4 · 2025-10-20T07:08:05Z

packages/platform-browser/src/dom/shared_styles_host.ts

 */
 interface UsageRecord<T> {
-  elements: T[];
+  elements: Map</** Host */ Node, /** Style Node */ T>;


Why do we need a Map here?

It was the data structure that was ported from the original commit that was reverted:

angular/packages/platform-browser/src/dom/shared_styles_host.ts

Line 19 in b63354e

elements: Map</** Host */ Node, /** Style Node */ HTMLStyleElement>;

What would you propose instead, just a plain object?

This code has been refactored greatly over the past year or so, and from what I am seeing elements: T[]; can be retained as the data structure as mostly I am seeing elements.values() which makes using a Map redundant here.

What about here when we remove the host?

angular/packages/platform-browser/src/dom/shared_styles_host.ts

Lines 259 to 261 in 39bb013

for (const {elements} of [...this.inline.values(), ...this.external.values()]) {

elements.delete(hostNode);

}

the removeHost is used used only in the ShadowDomRenderer, and in this case both this.inline and this.external will not be populated for the host that was added via addHostas addStyles and removeStyles are not used for shadow dom.

Makes sense, thank you! Fixed in 035ae4a (#64524)

thePunderWoman · 2025-10-20T17:18:39Z

@mattlewis92 This will likely have an impact on the new animate.enter and animate.leave APIs. We have issues where style sheets were getting prematurely pruned before when elements were removed. Unfortunately this is not the type of behavior that's easy to unit test. Can you verify this has no impact on that use case? We don't want styles disabled for elements that are in the process of animating away.

mattlewis92 · 2025-10-21T07:47:27Z

@mattlewis92 This will likely have an impact on the new animate.enter and animate.leave APIs. We have issues where style sheets were getting prematurely pruned before when elements were removed. Unfortunately this is not the type of behavior that's easy to unit test. Can you verify this has no impact on that use case? We don't want styles disabled for elements that are in the process of animating away.

Sure I can test that - do you have any kind of animations playground setup / reproduction of the previous issue where I can test it against?

thePunderWoman

This looks good to me. I think since you're re-using existing codepaths, this shouldn't have any impact on the animations use case. So we should be good.

JeanMeche · 2025-10-24T20:28:44Z

I'll take care of running a TGP over the weekend.

JeanMeche · 2025-10-27T00:36:06Z

TGP is failing. removeStyles has some usages, because even though ɵSharedStylesHost is private its pulled by at least one project.

mattlewis92 · 2025-10-27T10:21:24Z

TGP is failing. removeStyles has some usages, because even though ɵSharedStylesHost is private its pulled by at least one project.

Would it make sense to rename disableStyles back to removeStyles, or are you able to easily clean this up internally?

thePunderWoman · 2026-01-09T17:16:08Z

Heads up that this is likely to end up conflicting with #66048 which is being implemented by @dgp1130.

mattlewis92 · 2026-01-09T17:42:19Z

@thePunderWoman was the internal usage of the addStyles api cleaned up yet to unblock this PR? Looks like the signature of addStyles is changing in #66048 as well, so I guess it will need to be cleaned up to unblock both PRs

thePunderWoman · 2026-01-09T17:54:09Z

@mattlewis92 I'm unaware of the addStyles cleanup issue. Is there an open issue associated?

mattlewis92 · 2026-01-09T17:55:20Z

@mattlewis92 I'm unaware of the addStyles cleanup issue. Is there an open issue associated?

Just basing it on this comment from above:

TGP is failing. removeStyles has some usages, because even though ɵSharedStylesHost is private its pulled by at least one project.

thePunderWoman · 2026-01-09T17:58:21Z

@mattlewis92 Ah, I see. No, to my knowledge that has not changed.

JeanMeche · 2026-03-06T13:38:56Z

You might have only run the node test targets and the not browser test targets ?
pnpm bazel test //packages/core/test/acceptance:acceptance_web_chromium should pass locally (the firefox are always broken locally), It fails for me.

mattlewis92 · 2026-03-06T14:47:37Z

OK I think it's fixed now - the remaining test passes on my local machine, so I guess it's flakey?

Starting local Bazel server (8.6.0) and connecting to it...
INFO: Analyzed target //devtools/projects/ng-devtools-backend/src/lib/component-tree:test_firefox (1054 packages loaded, 47300 targets configured).
INFO: Found 1 test target...
Target //devtools/projects/ng-devtools-backend/src/lib/component-tree:test_firefox up-to-date:
  dist/bin/devtools/projects/ng-devtools-backend/src/lib/component-tree/test_firefox_/test_firefox
INFO: Elapsed time: 147.040s, Critical Path: 40.79s
INFO: 7703 processes: 2400 internal, 1466 darwin-sandbox, 3548 local, 289 worker.
INFO: Build completed successfully, 7703 total actions
//devtools/projects/ng-devtools-backend/src/lib/component-tree:test_firefox PASSED in 8.8s

Executed 1 out of 1 test: 1 test passes.

JeanMeche · 2026-03-06T14:48:49Z

This one is flakey yes.

mattlewis92 · 2026-03-06T15:59:57Z

Looks like the presubmit passed! 🚀

JeanMeche · 2026-03-06T16:14:25Z

I'm seeing some slight changes on some screenshot tests but I wouldn't consider them minor. No sure they're flakey.

mattlewis92 · 2026-03-06T17:08:39Z

Anything you're able to share to help me debug it? (I'm in the angular slack if you want to DM it to keep it private)

JeanMeche · 2026-03-09T10:43:21Z

Had a quick chat with Matt, this is probably a breaking change as the order of the styles elements might be different with this change.

Can you update the commit and the PR to reflect that Matt ? Thanks

mattlewis92 · 2026-03-09T11:56:17Z

Done!

mattlewis92 · 2026-03-09T15:22:40Z

The CI failure looks unrelated to this change, it wasn't failing on Friday, and I don't think this PR added more than 5kb of code to exceed the bundle budget threshold

thePunderWoman · 2026-04-10T15:30:45Z

@mattlewis92 Quick update: the reason for the delayed review is that @dgp1130 has been working on a style encapsulation PR for a while, and I was worried this would throw a wrench into his work. Once his stuff has landed, I can take a look.

JeanMeche · 2026-04-12T21:58:43Z

We'll need a rebase after the latest changes we did on the SharedStylesHost.

…of removing When a component is destroyed, instead of removing its style elements from the DOM, we now disable them. This avoids expensive style recalculations triggered by DOM removal while still preventing the styles from applying. When the same component is re-created, the styles are re-enabled.

mattlewis92 · 2026-04-13T08:57:23Z

We'll need a rebase after the latest changes we did on the SharedStylesHost.

Done!

thePunderWoman

LGTM

thePunderWoman · 2026-04-13T22:47:19Z

packages/platform-browser/src/dom/dom_renderer.ts

+    // no-op. This is necessary because `BaseAnimationRenderer.destroy()` defers
+    // `delegate.destroy()` via `afterFlushAnimationsDone` + `queueMicrotask`.
+    // Without this, the deferred `disableStyles()` would find the *replacement*
+    // component's newly-added style record (same content key) and disable it.


Can we add a TODO to clean this up after the legacy animation package is removed?

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	for (const {elements} of [...this.inline.values(), ...this.external.values()]) {
	elements.delete(hostNode);
	}

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mattlewis92 commented Oct 19, 2025 •

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