Converts an array of arrays of values to a CSV string.

toCSV.js

/**
 * @preserve Copyright (c) 2019 Christopher West
 * Licensed under the MIT license.
 */
/**
 * Converts an array of arrays of values to a CSV string.
 * @param {any[][]} rows
 *     An array of arrays of values that should be converted to a CSV string.
 * @param {Object} opt_options
 * @param {string=} opt_options.nullString
 *   This value will be used as the string that will appear whenever `null` or
 *   `undefined` is found (as long as `valueOf()` isn't defined).
 * @param {string[]=} opt_options.headers
 *   Optional array of headers that will appear on the first row.
 * @param {((value: any, row: number, col: number, rows) => any)=} opt_options.valueOf
 *   Optional function run for each cell value in rows to get the value that
 *   will be shown in the output CSV code.
 * @returns {string}
 *     The CSV version of `rows` with any specified options.
 */
function toCSV(rows, opt_options) {
  let {headers, nullString, valueOf} = Object(opt_options);
  if (headers) {
    rows = [headers].concat(rows);
  }
  if (nullString == null) nullString = '(NULL)';
  return rows
    .map(function (row, rowIndex) {
      return row.map(function (cell, colIndex) {
        if (valueOf && (!headers || rowIndex)) {
          cell = valueOf.call(opt_options, cell, rowIndex, colIndex, rows);
        }
        cell = cell != null
          ? 'string' === typeof cell
            ? cell
            : 'function' === typeof cell.toString
              ? cell + ""
              : Object.prototype.toString.call(cell)
          : nullString;
        return /[",\n\r]/.test(cell) ? '"' + (cell).replace(/"/g, '""') + '"' : cell;
      }).join(',');
    })
    .join('\n');
}