Javascript Collection class

Collection.class.js

'use strict';

class Collection extends Array {
  query(pattern){
    var regex = new RegExp(pattern);
    return this.filter(function(entry){
      return regex.test(entry);
    });
  }

  unique() {
    return this.filter((value, index, self) => self.indexOf(value) === index);
  }

  onlyUnique() {
  var that = this;
    return that.filter(function(entry){
      return that.filter(function(entry1){
        return (entry === entry1);
      }).length === 1
    });
  }
}

/**

  Examples:
  
> var mycollection = new Collection('hello','hello world', 'hello');

> mycollection.query('hello');
>> Collection(3) ["hello", "hello world", "hello"]

> mycollection.query(' ');
>> Collection ["hello world"]

> mycollection.query('^hello$');
>> Collection(2) ["hello", "hello"]

> mycollection.query('^hello$').unique();
>> Collection ["hello"]

> mycollection.unique();
>> Collection(2) ["hello", "hello world"]

> mycollection.onlyUnique();
>> Collection ["hello world"]

*/