JavaScript function not recognized as a function in Dash AG Grid sparklines

A client has reported an issue where the function key in the formatter property for the agSparklineCellRenderer is not being recognized as a JavaScript function in enterprise sparklines. Instead, it is interpreted as a string, which leads to incorrect behavior.
Some properties in AG Grid take a JavaScript function as inputs according to the doc here

The issue occurs when using the following configuration in the AG Grid;

{
  "cellRenderer": "agSparklineCellRenderer",
  "cellRendererParams": {
    "sparklineOptions": {
      "type": "bar",
      "formatter": {"function": "params.value[0] < 0 ? {fill: #5470c6} : {fill: #a90000}"},
      "valueAxisDomain": [-15, 15],
      "paddingOuter": 0,
      "padding": {
        "top": 0,
        "bottom": 0
      },
      "label": {
        "enabled": true,
        "fontWeight": "bold",
        "placement": "outsideEnd"
      }
    }
  }
}

Reference Links:

https://community.plotly.com/t/aggrid-agsparklinecellrenderer-and-formatter-params/84780

https://dash.plotly.com/dash-ag-grid/javascript-and-the-grid#functions

Start with the agSparklineCellRenderer configuration and the Dash AG Grid JavaScript functions documentation linked in the issue. Reproduce the supplied sparkline setup and trace how the formatter value is passed to the enterprise sparkline. Done means the formatter is recognized as a JavaScript function rather than a string and the configuration behaves correctly.