Run results for: Array spread operator vs unshift vs push reverse in reduce

Test name	Executions per second
spread operator	15505971.0 Ops/sec
unshift	10954551.0 Ops/sec
push reverse	11854828.0 Ops/sec

spread operator

var arr = [
        {
            "opportunityId": 5943111,
            "findingList": [
                {
                    "findingId": 6919
					 }
				],
		  },
		  {
				"opportunityId": 5943111,
            "findingList": [
                {
                    "findingId": 6918,
						   "findingId": 6917
					 }
				]
		  }
]

arr.reduce((acc, findingInOpp) => [...findingInOpp.findingList.map(({ findingId }) => findingId), ...acc],[])

unshift

var arr = [
        {
            "opportunityId": 5943111,
            "findingList": [
                {
                    "findingId": 6919
					 }
				],
		  },
		  {
				"opportunityId": 5943111,
            "findingList": [
                {
                    "findingId": 6918,
						   "findingId": 6917
					 }
				]
		  }
]

arr.reduce((acc, findingInOpp) => {
	acc.unshift(...findingInOpp.findingList.map(({ findingId }) => findingId))
	return acc
},[])

push reverse

var arr = [
        {
            "opportunityId": 5943111,
            "findingList": [
                {
                    "findingId": 6919
					 }
				],
		  },
		  {
				"opportunityId": 5943111,
            "findingList": [
                {
                    "findingId": 6918,
						   "findingId": 6917
					 }
				]
		  }
]

arr.reduce((acc, findingInOpp) => {
	acc.push(...findingInOpp.findingList.map(({ findingId }) => findingId))
	return acc
},[]).reverse()

Run results for: Array spread operator vs unshift vs push reverse in reduce

Compare the new ES6 spread operator with unshift and push reverse inside reduce

spread operator

unshift

push reverse