code: function $concat(params) {
      if (
          Array.isArray(params) &&
          (params.every(p => typeof p === 'string') ||
              params.every(p => Array.isArray(p)))
      ) {
          return params[0].concat(...params.slice(1));
      }
      throw new Error('$concat expects an array of array or string');
  }
docs: Concat strings or arrays
  
  @param {string[]|[][]} params
  @returns {string|any[]}