Clientside callback example with .js function throws “cannot read property ‘apply’ of undefined” error

Hi,
I’ve tried to use the cannonical examples given for the clientside callbacks using a js function.

The code I’m using is exactly the one prescribed:

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


app = dash.Dash(__name__)


app.layout = html.Div(children=
    [
        dcc.Input(id='input', value='hello world'),
        html.Div(id='output - clientside'),
        html.Div(id='output - serverside')
    ]
)

@app.callback(
    Output('output - serverside', 'children'),
    [Input('input', 'value')])
def update_output(value):
    return 'Server says “{}”'.format(value)

app.clientside_callback(
    output=Output('output - clientside', 'children'),
    inputs=[Input('input', 'value')],
    clientside_function = ClientsideFunction(
        namespace='clientside',
        function_name ='display'
    )
)


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

The display.js function sits in the /assets folder and is as foolows:

if(!window.dash_clientside) {window.dash_clientside = {};}
window.dash_clientside.clientside = {
    display: function (value) {
        return 'Client says "' + value + '"';
    }
}
}

Any help would be welcome since I need to accelerate some of my objects’ rendering by sending them to the client side.
Thanks.

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