Please don't load unused extension on the client side

If I have a multiple page the extensions like Plotly used on one page is also loaded on the other pages. This slows down the launch of the other pages, it does not add positively to the user experience and it means I have to spend more money on servers.

Please make it possible not to load unused extensions.

I would like to document the solution in #4281

Example

panel serve home.py dashboard.py --index home --autoreload

Open the Dashboard page at http://localhost:5006/dashboard
Open the Home page at http://localhost:5006
Open the developer tools and navigate to the network tab
Hard refresh the page by holding the Ctrl key and clicking the Refresh button
Sort the table by Time desc

Verify that plotly-2.10.1-min.js is loaded even though its not needed on the home page.

home-developer-tools

# home.py
import panel as pn

pn.extension(sizing_mode="stretch_width")

SECTION = """
Panel works really well with the visualization tools you already know and love like [Altair/ Vega](https://panel.holoviz.org/reference/panes/Vega.html), [Bokeh](https://panel.holoviz.org/reference/panes/Bokeh.html), [Datashader](https://datashader.org/), [Deck.gl/ pydeck](https://panel.holoviz.org/reference/panes/DeckGL.html), [Echarts/ pyecharts](https://panel.holoviz.org/reference/panes/ECharts.html), [Folium](https://panel.holoviz.org/reference/panes/Folium.html), [HoloViews](https://holoviews.org/), [hvPlot](https://hvplot.holoviz.org), [plotnine](https://panel.holoviz.org/reference/panes/Matplotlib.html), [Matplotlib](https://panel.holoviz.org/reference/panes/Matplotlib.html), [Plotly](https://panel.holoviz.org/reference/panes/Plotly.html), [PyVista/ VTK](https://panel.holoviz.org/reference/panes/VTK.html), [Seaborn](https://panel.holoviz.org/gallery/styles/SeabornStyle.html) and more. Panel also works with the [ipywidgets](https://panel.holoviz.org/reference/panes/IPyWidget.html) ecosystem.
"""

IMAGE = pn.pane.GIF("https://user-images.githubusercontent.com/42288570/211983400-3315ad0a-866a-4916-8809-6fc38eca34d9.gif", alt_text="Pythons DataViz works with Panel", link_url="https://panel.holoviz.org/reference/index.html#panes", height=400)

component = pn.Column(
    SECTION, IMAGE
)

NAVIGATION = """
## Navigation

[home](home)
[dashboard](dashboard)
"""

pn.template.FastListTemplate(
    site="Panel", site_url="https:\\panel.holoviz.org",
    title="Home", main=[component], sidebar=[NAVIGATION],
    main_max_width="900px",
).servable()

import panel as pn
import pandas as pd
import plotly.graph_objects as go

from bokeh.sampledata import stocks

pn.extension('plotly')

title = '## Stock Explorer Plotly'

tickers = ['AAPL', 'FB', 'GOOG', 'IBM', 'MSFT']

SOURCES = {
    "AAPL": "http://sampledata.bokeh.org/AAPL.csv",
    "FB": "http://sampledata.bokeh.org/FB.csv",
    "GOOG": "http://sampledata.bokeh.org/GOOG.csv",
    "IBM": "http://sampledata.bokeh.org/IBM.csv",
    "MSFT": "http://sampledata.bokeh.org/MSFT.csv",
}

def get_df(ticker, window_size):
    url = SOURCES[ticker]
    df = pd.read_csv(url)
    df = df.rename(columns={"Date": "date", "Close": "close"})
    df['date'] = pd.to_datetime(df.date)
    return df.set_index('date').rolling(window=window_size).mean().reset_index()

ticker = pn.widgets.Select(name='Ticker', options=tickers)
window = pn.widgets.IntSlider(name='Window Size', value=6, start=1, end=21)

def get_plot(ticker, window_size):
    df = get_df(ticker, window_size)
    return go.Scatter(x=df.date, y=df.close)

component = pn.Column(
    pn.Column(title, ticker, window),
    pn.bind(get_plot, ticker, window),
    sizing_mode='stretch_width'
)

NAVIGATION = """
## Navigation

[home](/)
[dashboard](dashboard)
"""

pn.template.FastListTemplate(
    site="Panel", site_url="https:\\panel.holoviz.org",
    title="Dashboard", main=[component], sidebar=[NAVIGATION],
    main_max_width="900px",
).servable()

holoviz / panel

Please don't load unused extension on the client side #4282

Example