code: function count(predicate) {
    predicate = typeof predicate === 'function' ? predicate : util.defaultPredicate;
  
    let c = 0;
  
    for (let item of this) {
      if (predicate(item)) c++;
    }
  
    return c;
  }
docs: Returns a number that represents how many elements in the specified sequence satisfy a condition.
  
  @param {(Function)} predicate The condition for compute item counts
  @return Return the count which satisfy a condition.