简单的问题使用Dash，我如何显示变量的更新输出？

import dash
import dash_core_components as dcc
import dash_html_components as html
from dash.dependencies import Input, Output

app = dash.Dash(__name__)

app.layout = html.Div([
    html.Button('点击更新', id='update-button'),
    html.Div(id='output-div')
])

@app.callback(
    Output('output-div', 'children'),
    [Input('update-button', 'n_clicks')]
)
def update_output(n_clicks):
    if n_clicks is None:
        return '尚未点击更新按钮'
    else:
        return f'已点击更新按钮 {n_clicks} 次'

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