code: function coordinates(index, source) {
      if (!index || !source)
          return void 0;
  
      var lines = source
              .slice(0, index)
              .split('\n');
  
      return lines.length + ':' + lines.pop().length;
  }
docs: Get row and column number in given string at given index.
  
  @param  {Number} index
  @param  {String} source
  @return {String}
  @api private