[BUG] set_props streaming

In Dash 4.5.0:

A streaming callback does not send set_props to the client until the next yield.

Below is an example app:

from dash import LocalSharedStorage, Dash, html, dcc, Input, Output, callback, set_props, no_update
import asyncio

app = Dash(__name__,
           shared_storage=LocalSharedStorage())

app.layout = html.Div([
    html.Button(id='input', type='button', children='Click Me'),
    html.Div(id='output')
])

@callback(
    Output('output', 'id'),
    Input('input', 'n_clicks'),
    prevent_initial_call=True
)
async def update_output(value):
    set_props('output', {'children': html.Div(id='output2', children='Loading...')})
    # yield no_update
    await asyncio.sleep(1)
    set_props('output2', {'children': f'You entered: {value}'})
    yield no_update

if __name__ == '__main__':
    app.run(debug=True)

Here is a helper function that can create passive responses for the time-being:

def make_no_update_response(ctx):
    # Return a no_update payload that matches the callback output shape.
    outputs_list = getattr(ctx, "outputs_list", None)
    if isinstance(outputs_list, list) and outputs_list:
        return [no_update for _ in outputs_list]

    outputs_grouping = getattr(ctx, "outputs_grouping", None)
    if isinstance(outputs_grouping, list):
        return [no_update for _ in outputs_grouping]
    if isinstance(outputs_grouping, tuple):
        return tuple(no_update for _ in outputs_grouping)
    if isinstance(outputs_grouping, dict):
        return {k: no_update for k in outputs_grouping}

    body = getattr(ctx, "body", None)
    if isinstance(body, dict):
        outputs = body.get("outputs")
        if isinstance(outputs, list):
            return [no_update for _ in outputs]

    return no_update

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[BUG] `set_props` streaming #4127

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[BUG] set_props streaming #4127

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BSd3v commented on Nov 6, 2026

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[BUG] `set_props` streaming #4127