A custom function for Google Sheets to turn a spreadsheet range into a Markdown Table

sheetToMarkdownTable.gs

/**
 * Produced a table in markdown format
 *
 * @param {Range} inputRange The range of data to markdown-ify
 * @param {boolean} includesHeader does the data have a header? defaults to true.
 * @return {string} Range in markdown table format.
 * @customfunction
 */
function markdownTable(inputRange, includesHeader = true) {
  let tableOutput = '';
  for (row in inputRange) {
    tableOutput += processTableRow(inputRange[row])
    if (includesHeader && row == 0) {
      tableOutput += markdownHeaderBreak(inputRange[row].length);
    }
  }
  return tableOutput
}

/**
 * Produces a pipe (|) delimited string
 * @param {number} columns The number of columns in the table
 * @return {string}
 */
function markdownHeaderBreak(columns) {

  let headerBreak = '|';
  for (let i = 0; i < columns; i++) {
    headerBreak += '---|';
  }
  return headerBreak + '\n';
}

/** 
 * Wraps a table row in pipes (|) and replaces any line breaks with html <br /> tags
 * @param {array} row A 1D array of data
 * @return {string} 
 */
function processTableRow(row) {
  let tableRow = '|';
  for (column in row) {
    let colString = String(row[column]);
    tableRow += colString.replace(/\n/ig, '<br />') + '|';
  }
  return tableRow + '\n';
}