Adding pagination to knex.js

knex-pagination.js

module.exports = function(dbConfig) {
	var knex = require('knex')(dbConfig);

	var KnexQueryBuilder = require('knex/lib/query/builder');

	KnexQueryBuilder.prototype.paginate = function (per_page, current_page) {
		var pagination = {};
		var per_page = per_page || 10;
		var page = current_page || 1;
		if (page < 1) page = 1;
		var offset = (page - 1) * per_page;
		return Promise.all([
				this.clone().count('* as count').first(),
				this.offset(offset).limit(per_page)
			])
			.then(([total, rows]) => {
				var count = total.count;
				var rows = rows;
				pagination.total = count;
				pagination.per_page = per_page;
				pagination.offset = offset;
				pagination.to = offset + rows.length;
				pagination.last_page = Math.ceil(count / per_page);
				pagination.current_page = page;
				pagination.from = offset;
				pagination.data = rows;
				return pagination;
			});
	};

	knex.queryBuilder = function () {
		return new KnexQueryBuilder(knex.client);
	};

	return knex;
}

Why do we need to re-instantiate knex's querybuilder? (i.e. this code below)

knex.queryBuilder = function () {
  return new KnexQueryBuilder(knex.client);
};

Doesn't changing the prototype for the QueryBuilder affect the existing instance?
And it seems to be working fine without this last part!