assert on websocket frames in a playwright test using page.waitforevent('websocket')
domain: playwright.dev · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
start the promise for page.waitForEvent('websocket') before triggering the action that opens the WebSocket connection
trigger the page action (e.g. a button click or page.evaluate that opens `new WebSocket(...)`) inside a Promise.all alongside the waitForEvent call
once resolved, use the returned WebSocket handle's waitForEvent('framesent') or waitForEvent('framereceived') with a predicate to assert on specific payloads
optionally call webSocket.waitForEvent('close') to assert the connection is torn down cleanly at the end of the flow
set an explicit timeout on waitForEvent calls since the default in some APIs is no timeout
Known gotchas
the 'websocket' event only fires once when the WebSocket is created, so the wait must be armed before the connection-opening action runs or it will be missed
for deterministic mocking instead of observation, page.routeWebSocket() is the appropriate tool rather than waitForEvent
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