for(let i=0; i < columns.length; i++){
    columns[i] = resolveProps(columns[i], ["formatter"])
} 

window.myNamespace = Object.assign({}, window.myNamespace, {
    tabulator: {
        printIcon: function (cell, formatterParams, onRendered) {
            return "<i class='fa fa-print'></i>";
        }
    }
});

from dash_extensions.javascript import Namespace
...
ns = Namespace("myNamespace", "tabulator")
...
columns = [{"formatter": ns("printIcon")}, ...]

import dash_tabulator
import dash
import dash_html_components as html
from dash_extensions.javascript import Namespace

# The namespace here must match the name space of the JavaScript asset.
ns = Namespace("myNamespace", "tabulator")
# Setup some data
columns = [
    {"title": "Name", "field": "name", "width": 150, "headerFilter": True, "editor": "input"},
    {"title": "Print", "field": "print", "hozAlign": "center", "formatter": ns("printIcon")}
]
data = [
    {"id": 1, "name": "Oli Bob", "print": "stuff1"},
    {"id": 2, "name": "Mary May", "print": "stuff2"},
]
# Create example app.
external_stylesheets = ['https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css',
                        'https://cdnjs.cloudflare.com/ajax/libs/font-awesome/5.15.1/css/all.min.css']
app = dash.Dash(__name__, external_stylesheets=external_stylesheets)
app.layout = html.Div([
    dash_tabulator.DashTabulator(id='tabulator', columns=columns, data=data),
])

if __name__ == '__main__':
    app.run_server(debug=False, port=7777)