I have a JS file that is called in a python-based bokeh app. The JS file produces a download button to get a csv of the data used in the interactive charts made by the app. The data contain dates and integers. How can I get the downloaded csv to include the formatting for the dates?

This is the JS file.

function table_to_csv(source) {
  const columns = Object.keys(source.data)
  const nrows = source.get_length()
  const lines = [columns.join('`').replaceAll(/,/g,' ').replaceAll(/`/g,',')]
  
  for (let i = 0; i < nrows; i++) {
    let row = [];
    for (let j = 0; j < columns.length; j++) {
      const column = columns[j]
      const val = source.data[column][i]
      if (column == 'Date'){
        row.push(val.getDate() +'/'+(val.getMonth()+1)+'/'+val.getFullYear()}
      else
        row.push(val.toString())
    }
    lines.push(row.join(','))
  }
  return lines.join('\n').concat('\n')
}


const filename = 'data/survey_results.csv'
const filetext = table_to_csv(source)
const blob = new Blob([filetext], { type: 'text/csv;charset=utf-8;' })

//addresses IE
if (navigator.msSaveBlob) {
  navigator.msSaveBlob(blob, filename)
} else {
  const link = document.createElement('a')
  link.href = URL.createObjectURL(blob)
  link.download = filename
  link.target = '_blank'
  link.style.visibility = 'hidden'
  link.dispatchEvent(new MouseEvent('click'))
}

The date format in the csv used for the charts is d/m/y.