fix: anywidget refresh value#9454
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…of being dropped.
… events after widget render completes.
…ckend updates arrive before render listeners attached, it doesn't cause a state mismatch.
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1 issue found across 6 files
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<file name="marimo/_plugins/ui/_impl/comm.py">
<violation number="1" location="marimo/_plugins/ui/_impl/comm.py:123">
P3: Update `_create_model_message` docstring: it still says `echo_update` is skipped, but this branch now emits a `ModelUpdate`.</violation>
</file>
Architecture diagram
sequenceDiagram
participant UI as Widget UI (FE)
participant Plugin as AnyWidgetPlugin
participant Model as Frontend Model
participant Comm as Marimo Comm (BE)
participant Kernel as Python Kernel
Note over UI, Kernel: Phase 1: State Capture (During Interaction)
UI->>Model: model.set("count", 8)
Model->>Comm: sendUpdate({ method: "echo_update", state: {count: 8} })
rect rgb(240, 240, 240)
Note over Comm: CHANGED: Handle "echo_update"
Comm->>Comm: Create ModelUpdate message
Note right of Comm: Prevents dropping state<br/>on acknowledgement path
end
Comm-->>Kernel: Broadcast state to all clients
Note over UI, Kernel: Phase 2: State Hydration (Upon Notebook Reload)
Kernel->>Comm: Replay stored state
Comm->>Model: updateAndEmitDiffs({ count: 8 })
Plugin->>Plugin: bind(widgetDef, model)
Plugin->>UI: render(element, model)
alt Widget Initialization
UI->>Model: model.on("change:count", listener)
Note left of UI: Widget defaults to "5"<br/>(Internal initial state)
end
rect rgb(240, 240, 240)
Note over Plugin, Model: NEW: Re-hydration Flow
Plugin->>Model: getMarimoInternal(model).reemitState()
loop For each key in state
Model->>UI: emit("change:count", 8)
end
Model->>UI: emit("change")
end
UI->>UI: listener updates UI to "8"
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Fix all with cubic.
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Pull request overview
Fixes anywidget model state hydration on browser refresh/reconnect by ensuring frontend-originated state changes are preserved for session replay and by re-emitting the current model state after a widget view attaches listeners.
Changes:
- Backend: treat
echo_updatemessages asModelUpdateso they are included in replayable model state. - Frontend: add an internal
reemitState()API to re-dispatch current model values aschange:*events afterrender(). - Tests: add backend and frontend test coverage for
echo_updatereplay contribution and late listener hydration.
Reviewed changes
Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.
Show a summary per file
| File | Description |
|---|---|
marimo/_plugins/ui/_impl/comm.py |
Converts echo_update into ModelUpdate to preserve state for reconnect replay. |
tests/_plugins/ui/_impl/test_comm.py |
Adds coverage ensuring echo_update is broadcast as a state-bearing update. |
frontend/src/plugins/impl/anywidget/model.ts |
Adds internal reemitState() that emits change:* events for current state. |
frontend/src/plugins/impl/anywidget/AnyWidgetPlugin.tsx |
Calls reemitState() after render() so late listeners observe hydrated state. |
frontend/src/plugins/impl/anywidget/__tests__/model.test.ts |
Tests reemitState() emits field and aggregate change events. |
frontend/src/plugins/impl/anywidget/__tests__/AnyWidgetPlugin.test.tsx |
Adds regression test for hydration when listener attaches after initial state is set. |
Comment on lines
122
to
+126
| elif method == "echo_update": | ||
| # echo_update is for multi-client sync acknowledgment, skip it | ||
| return None | ||
| # Preserve frontend-driven trait changes for reconnect replay. | ||
| # anywidget/ipywidgets can emit echo_update as the synchronisation | ||
| # acknowledgement path; dropping it causes stale replay state. | ||
| return ModelUpdate( |
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Hello @manzt
If you could take a look at this, before it becomes stale, that would be great.
Thank you
Bundle ReportChanges will increase total bundle size by 140 bytes (0.0%) ⬆️. This is within the configured threshold ✅ Detailed changes
Affected Assets, Files, and Routes:view changes for bundle: marimo-esmAssets Changed:
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📝 Summary
The Counter anywidget was always defaulting to a default value of
5upon reloading the notebook as the state wasn't being reattached to the FE. This fixes the issue by sending anecho_updateto BE and upon reload reconnects to get the correct state. FE callsreemitStateensure that all listeners receive the state even if one was rendered before the other.Closes #9420
Screen.Recording.2026-05-04.at.17.29.29.mov
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