a.js

// using array

const bluebird = require('bluebird')
const things = [{a: 1}, {b: 2}, {c: 3}]

function doit(doc) {
	return bluebird.delay(1000).then(() => {return doc})
}

async function main() {
	console.time('abc')
	const results = [], len = things.length
	for(var i=0;i<3;i++) {
		results.push(await doit(things[i]))
	}
	console.log(results)
	console.timeEnd('abc')
}

main()

// [ { a: 1 }, { b: 2 }, { c: 3 } ]
// abc: 3015.500ms

b.js

// using Promise.all

var bluebird=require('bluebird')
var things = [{a: 1}, {b: 2}, {c: 3}]

function doit(doc) {
	return bluebird.delay(1000).then(() => {return doc})
}

async function main() {
	console.time('abc')
	const results = await Promise.all(things.map(doit))
	console.log(results)
	console.timeEnd('abc')
}

main()


// [ { a: 1 }, { b: 2 }, { c: 3 } ]
// abc: 1007.932ms