Enable third party components to trigger actions like download

[chriddyp]

If we had a property like n_downloaded that represents the "number of times the data has been downloaded", then users could wire in their own components like buttons to trigger downloads. For example:

html.Button('Download Data', id='download'),
data_table.DataTable(id='table', ...),

@app.callback(Output('table', 'n_downloaded'), [Input('download', 'n_clicks')])
def trigger_download(n_clicks):
    return n_clicks

[chriddyp]

Alternatively, this could be a first class component of DataTable, like dash_table.Download with a target ID:

dash_table.Download(html.Button('Download'), target='table'),
dash_table.DataTable(id='table')

and the implementation could just bind the DataTable's download function to a window function or an event listener, scoped by component ID.