code: function getArrayFields(array) {
      return (array || []).reduce((old, current) => {
          arrayDiff(Object.keys(current), old)
              .forEach(key => old.push(key));
  
          return old;
      }, []);
  }
docs: Retrieves every field in the array of objects. These are collected in a Hash-map which means they are unique.
  
  @param {array} array Subject of the operation
  @returns {array}