team-up.js

'use strict'

const _ = require('lodash')

const teams = _.range(1, 20)
const chunkSize = 5

const {groupings} = _(teams)
	.map((team) => ({ number: team, order: Math.random() }))
	.sortBy('order')
	.reduce(({ groupings, chunk }, { number, order }) => {
		groupings[groupings.length - 1].push(number)
		if(chunk >= chunkSize) {
			groupings.push([])
			return { groupings, chunk: 0 }
		} else {
			chunk += 1
			return { groupings, chunk }
		}
	}, { groupings: [[]], chunk: 0 })

console.log(groupings)