title: How to use a button to trigger callback updates?
body: <p>I am just getting started with dash. Taking the example from <a href="https://plot.ly/dash/getting-started-part-2#interactivity" rel="noreferrer">here</a>. I want to convert the dash app below</p>
  
  <pre><code>import dash
  from dash.dependencies import Input, Output
  import dash_core_components as dcc
  import dash_html_components as html
  
  app = dash.Dash()
  
  app.layout = html.Div([
      dcc.Input(id='my-id', value='initial value', type="text"),
      html.Div(id='my-div')
  ])
  
  @app.callback(
      Output(component_id='my-div', component_property='children'),
      [Input(component_id='my-id', component_property='value')]
  )
  def update_output_div(input_value):
      return 'You\'ve entered "{}"'.format(input_value)
  
  if __name__ == '__main__':
      app.run_server()
  </code></pre>
  
  <p>To update when the user presses a button not when the value of the input field changes. How do I accomplish this? </p>