override request get/set query method to allow comma notation in query params

koa-query-string.ts

import merge from 'merge-descriptors';
import qs from 'qs';
import Application from 'koa';

// eslint-disable-next-line func-names
module.exports = function(app: Application) {
  merge(app.request, {
    get query() {
      const str = this.querystring;
      if (!str) {
        return {};
      }
      this._querycache = this._querycache || {};
      const cache = this._querycache;

      let query = cache[str];
      if (!query) {
        query = qs.parse(str, { comma: true });
        // optional delete if not needed
        Object.keys(query).forEach(key => {
          if (query[key] instanceof String) {
            query[key] = query[key].trim();
          }

          if (query[key] instanceof Array) {
            query[key] = query[key]
              .map((param: string) => param.trim())
              .filter((param: string) => param !== '');
          }
        });

        cache[str] = query;
      }
      return query;
    },

    set query(obj) {
      this.querystring = qs.stringify(obj);
    },
  } as any);

  return app;
};