Google Sheets custom function: Get a link from a given cell.

GoogleSheets-getCellLink.gs

/** 
 * Extracts the first text string in double quotes in the formula of the cell at given address.
 * @param {"A1"}  address Cell address as a string.
 * @customfunction
 */
function getCellLink(address) {

  if(!(address && typeof(address) == 'string'))
    throw new Error('The 1st param must be a cell address as a string.');

  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var cell = ss.getRange(address);
  var url = cell.getRichTextValue().getLinkUrl()

  if (!url) 
    throw new Error('The cell in ' + address + ' does not contain a link.');
  
  return url
}