Really needing help to understand this concept of this package

Dash Python
1

Situation1, I have two callbacks:

@callback(
    Output('hover-data', 'children'),
    Input('basic-interactions', 'hoverData'))
def display_hover_data(hoverData):
    return str(hoverData)

@callback(
    Output('click-data', 'children'),
    Input('basic-interactions', 'clickData'))
def display_click_data(clickData):
    return json.dumps(clickData, indent=2)

Situation2, I have one callback:

@callback(
    Output('hover-data', 'children'),
    Input('basic-interactions', 'hoverData'))
def display_hover_data(hoverData):
    return str(hoverData)

I rewrite the object Dash’s method dispatch:

    def write_info(self, info):
        file = open('/root/arcta/notebook/comp/exx.txt', 'a')
        file.write(f"{info}\n")
        file.close()

    def dispatch(self):
        self.write_info("aa---")
        body = flask.request.get_json()
        self.write_info(str(body))
        self.write_info("bb")

In situation1, when I hover a data or click a data, the method dispatch will run. But in situation2, when I click a data, the method dispatch will not run. It seems the macro callback register a EventLisener to the code from the webpage. But where is the code that register the EventLisener to the web? How does it make the post on _dash-update-component decide that when clicking a data, it will not make a request?