function arrayDiff( a1, a2) {
	var common = []
	var a1only = []
	var a2only = [].concat(a2)

	a1.forEach( e=>{
		if (a2only.includes(e)) {
			common.push(e)
			a2only.splice( a2only.indexOf(e), 1)
		} else {
			a1only.push(e)
		}
	})

	return { common, a1only, a2only}
}