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fix(browser): Use current start timestamp for CLS span when CLS is 0 #17800

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Merged
merged 1 commit into from
Sep 29, 2025
Merged

fix(browser): Use current start timestamp for CLS span when CLS is 0 #17800

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12 changes: 8 additions & 4 deletions packages/browser-utils/src/metrics/cls.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@ import {
SEMANTIC_ATTRIBUTE_SENTRY_MEASUREMENT_VALUE,
SEMANTIC_ATTRIBUTE_SENTRY_OP,
SEMANTIC_ATTRIBUTE_SENTRY_ORIGIN,
timestampInSeconds,
} from '@sentry/core';
import { DEBUG_BUILD } from '../debug-build';
import { addClsInstrumentationHandler } from './instrument';
Expand Down Expand Up @@ -42,28 +43,31 @@ export function trackClsAsStandaloneSpan(client: Client): void {
}, true);

listenForWebVitalReportEvents(client, (reportEvent, pageloadSpanId) => {
sendStandaloneClsSpan(standaloneCLsValue, standaloneClsEntry, pageloadSpanId, reportEvent);
_sendStandaloneClsSpan(standaloneCLsValue, standaloneClsEntry, pageloadSpanId, reportEvent);
cleanupClsHandler();
});
}

function sendStandaloneClsSpan(
/**
* Exported only for testing!
*/
export function _sendStandaloneClsSpan(
clsValue: number,
entry: LayoutShift | undefined,
pageloadSpanId: string,
reportEvent: WebVitalReportEvent,
) {
DEBUG_BUILD && debug.log(`Sending CLS span (${clsValue})`);

const startTime = msToSec((browserPerformanceTimeOrigin() || 0) + (entry?.startTime || 0));
const startTime = entry ? msToSec((browserPerformanceTimeOrigin() || 0) + entry.startTime) : timestampInSeconds();
const routeName = getCurrentScope().getScopeData().transactionName;

const name = entry ? htmlTreeAsString(entry.sources[0]?.node) : 'Layout shift';

const attributes: SpanAttributes = {
[SEMANTIC_ATTRIBUTE_SENTRY_ORIGIN]: 'auto.http.browser.cls',
[SEMANTIC_ATTRIBUTE_SENTRY_OP]: 'ui.webvital.cls',
[SEMANTIC_ATTRIBUTE_EXCLUSIVE_TIME]: entry?.duration || 0,
[SEMANTIC_ATTRIBUTE_EXCLUSIVE_TIME]: 0,
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those were just useless bytes. duration is always zero for CLS

// attach the pageload span id to the CLS span so that we can link them in the UI
'sentry.pageload.span_id': pageloadSpanId,
// describes what triggered the web vital to be reported
Expand Down
231 changes: 231 additions & 0 deletions packages/browser-utils/test/metrics/cls.test.ts
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Original file line number Diff line number Diff line change
@@ -0,0 +1,231 @@
import * as SentryCore from '@sentry/core';
import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
import { _sendStandaloneClsSpan } from '../../src/metrics/cls';
import * as WebVitalUtils from '../../src/metrics/utils';

// Mock all Sentry core dependencies
vi.mock('@sentry/core', async () => {
const actual = await vi.importActual('@sentry/core');
return {
...actual,
browserPerformanceTimeOrigin: vi.fn(),
timestampInSeconds: vi.fn(),
getCurrentScope: vi.fn(),
htmlTreeAsString: vi.fn(),
};
});

describe('_sendStandaloneClsSpan', () => {
const mockSpan = {
addEvent: vi.fn(),
end: vi.fn(),
};

const mockScope = {
getScopeData: vi.fn().mockReturnValue({
transactionName: 'test-transaction',
}),
};

afterEach(() => {
vi.clearAllMocks();
});

beforeEach(() => {
vi.mocked(SentryCore.getCurrentScope).mockReturnValue(mockScope as any);
vi.mocked(SentryCore.browserPerformanceTimeOrigin).mockReturnValue(1000);
vi.mocked(SentryCore.timestampInSeconds).mockReturnValue(1.5);
vi.mocked(SentryCore.htmlTreeAsString).mockImplementation((node: any) => `<${node?.tagName || 'div'}>`);
vi.spyOn(WebVitalUtils, 'startStandaloneWebVitalSpan').mockReturnValue(mockSpan as any);
});

it('sends a standalone CLS span with entry data', () => {
const clsValue = 0.1;
const mockEntry: LayoutShift = {
name: 'layout-shift',
entryType: 'layout-shift',
startTime: 100,
duration: 0,
value: clsValue,
hadRecentInput: false,
sources: [
// @ts-expect-error - other properties are irrelevant
{
node: { tagName: 'div' } as Element,
},
],
toJSON: vi.fn(),
};
const pageloadSpanId = '123';
const reportEvent = 'navigation';

_sendStandaloneClsSpan(clsValue, mockEntry, pageloadSpanId, reportEvent);

expect(WebVitalUtils.startStandaloneWebVitalSpan).toHaveBeenCalledWith({
name: '<div>',
transaction: 'test-transaction',
attributes: {
'sentry.origin': 'auto.http.browser.cls',
'sentry.op': 'ui.webvital.cls',
'sentry.exclusive_time': 0,
'sentry.pageload.span_id': '123',
'sentry.report_event': 'navigation',
'cls.source.1': '<div>',
},
startTime: 1.1, // (1000 + 100) / 1000
});

expect(mockSpan.addEvent).toHaveBeenCalledWith('cls', {
'sentry.measurement_unit': '',
'sentry.measurement_value': 0.1,
});

expect(mockSpan.end).toHaveBeenCalledWith(1.1);
});

it('sends a standalone CLS span without entry data', () => {
const clsValue = 0;
const pageloadSpanId = '456';
const reportEvent = 'pagehide';

_sendStandaloneClsSpan(clsValue, undefined, pageloadSpanId, reportEvent);

expect(SentryCore.timestampInSeconds).toHaveBeenCalled();
expect(SentryCore.browserPerformanceTimeOrigin).not.toHaveBeenCalled();

expect(WebVitalUtils.startStandaloneWebVitalSpan).toHaveBeenCalledWith({
name: 'Layout shift',
transaction: 'test-transaction',
attributes: {
'sentry.origin': 'auto.http.browser.cls',
'sentry.op': 'ui.webvital.cls',
'sentry.exclusive_time': 0,
'sentry.pageload.span_id': pageloadSpanId,
'sentry.report_event': 'pagehide',
},
startTime: 1.5,
});

expect(mockSpan.end).toHaveBeenCalledWith(1.5);
expect(mockSpan.addEvent).toHaveBeenCalledWith('cls', {
'sentry.measurement_unit': '',
'sentry.measurement_value': 0,
});
});

it('handles entry with multiple sources', () => {
const clsValue = 0.15;
const mockEntry: LayoutShift = {
name: 'layout-shift',
entryType: 'layout-shift',
startTime: 200,
duration: 0,
value: clsValue,
hadRecentInput: false,
sources: [
// @ts-expect-error - other properties are irrelevant
{
node: { tagName: 'div' } as Element,
},
// @ts-expect-error - other properties are irrelevant
{
node: { tagName: 'span' } as Element,
},
],
toJSON: vi.fn(),
};
const pageloadSpanId = '789';

vi.mocked(SentryCore.htmlTreeAsString)
.mockReturnValueOnce('<div>') // for the name
.mockReturnValueOnce('<div>') // for source 1
.mockReturnValueOnce('<span>'); // for source 2

_sendStandaloneClsSpan(clsValue, mockEntry, pageloadSpanId, 'navigation');

expect(SentryCore.htmlTreeAsString).toHaveBeenCalledTimes(3);
expect(WebVitalUtils.startStandaloneWebVitalSpan).toHaveBeenCalledWith({
name: '<div>',
transaction: 'test-transaction',
attributes: {
'sentry.origin': 'auto.http.browser.cls',
'sentry.op': 'ui.webvital.cls',
'sentry.exclusive_time': 0,
'sentry.pageload.span_id': '789',
'sentry.report_event': 'navigation',
'cls.source.1': '<div>',
'cls.source.2': '<span>',
},
startTime: 1.2, // (1000 + 200) / 1000
});
});

it('handles entry without sources', () => {
const clsValue = 0.05;
const mockEntry: LayoutShift = {
name: 'layout-shift',
entryType: 'layout-shift',
startTime: 50,
duration: 0,
value: clsValue,
hadRecentInput: false,
sources: [],
toJSON: vi.fn(),
};
const pageloadSpanId = '101';

_sendStandaloneClsSpan(clsValue, mockEntry, pageloadSpanId, 'navigation');

expect(WebVitalUtils.startStandaloneWebVitalSpan).toHaveBeenCalledWith({
name: '<div>',
transaction: 'test-transaction',
attributes: {
'sentry.origin': 'auto.http.browser.cls',
'sentry.op': 'ui.webvital.cls',
'sentry.exclusive_time': 0,
'sentry.pageload.span_id': '101',
'sentry.report_event': 'navigation',
},
startTime: 1.05, // (1000 + 50) / 1000
});
});

it('handles when startStandaloneWebVitalSpan returns undefined', () => {
vi.spyOn(WebVitalUtils, 'startStandaloneWebVitalSpan').mockReturnValue(undefined);

const clsValue = 0.1;
const pageloadSpanId = '123';

expect(() => {
_sendStandaloneClsSpan(clsValue, undefined, pageloadSpanId, 'navigation');
}).not.toThrow();

expect(mockSpan.addEvent).not.toHaveBeenCalled();
expect(mockSpan.end).not.toHaveBeenCalled();
});

it('handles when browserPerformanceTimeOrigin returns null', () => {
vi.mocked(SentryCore.browserPerformanceTimeOrigin).mockReturnValue(undefined);

const clsValue = 0.1;
const mockEntry: LayoutShift = {
name: 'layout-shift',
entryType: 'layout-shift',
startTime: 200,
duration: 0,
value: clsValue,
hadRecentInput: false,
sources: [],
toJSON: vi.fn(),
};
const pageloadSpanId = '123';

_sendStandaloneClsSpan(clsValue, mockEntry, pageloadSpanId, 'navigation');

expect(WebVitalUtils.startStandaloneWebVitalSpan).toHaveBeenCalledWith(
expect.objectContaining({
startTime: 0.2,
}),
);
});
});