Read browser results

NotebookView.state reports browser work as one consistent, read-only snapshot.

import observablejs as obs

notebook = obs.Notebook(
    obs.ojs(
        'viewof gain = Inputs.range([0, 12], {value: 5, step: 1, label: "Gain"})',
        key="gain_control",
    ),
    obs.js("const doubled = gain * 2;", key="doubled", display=False),
    obs.js(
        'html`<p>Gain is <strong>${gain}</strong>. Doubled is <strong>${doubled}</strong>.</p>`',
        key="readout",
    ),
)

view = notebook.view()
view

Read a result after the latest input revision settles. In marimo, reference view.value first so the reading cell reruns when the view synchronizes:

view.value  # rerun this cell when synchronized widget state changes
state = view.state

if (
    not state.pending
    and state.input_revision is not None
    and state.settled_revision == state.input_revision
):
    doubled = state.result("doubled")
    if doubled.status == "success":
        print(doubled.values["doubled"])
    else:
        print(doubled.errors)

Each CellResult has a status, revision, read-only values, and structured errors. A failed output reports its error phase and optional variable name. A multi-output cell may contain successful values beside errors.

React to state changes

Traitlets-aware environments can observe the public state trait:

def on_state(change):
    state = change["new"]
    if not state.pending:
        print(state.results)

view.observe(on_state, names="state")

In marimo, reference view.value in the reading cell so that the cell reruns when synchronized widget state changes, then read view.state.

State belongs to the view whose runtime produced it. A focused view reports its selected result while hidden dependencies still evaluate:

gain_view = notebook.view("gain_control")

See View state and graph for revision, status, error, and value conversion contracts.