grafana/public/app/core/utils/query.ts

import _ from 'lodash';
import { DataQuery } from '@grafana/data';

export const getNextRefIdChar = (queries: DataQuery[]): string => {
  const letters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';

  return (
    _.find(letters, refId => {
      return _.every(queries, other => {
        return other.refId !== refId;
      });
    }) ?? 'NA'
  );
};

export function addQuery(queries: DataQuery[], query?: Partial<DataQuery>): DataQuery[] {
  const q = query || {};
  q.refId = getNextRefIdChar(queries);
  return [...queries, q as DataQuery];
}