Example of Async/Await vs Promises vs Promise.all

AsyncAwait.js

// Async Await is syntactic sugar over promises
// They are not a complete replacement as you still need to construct Promise objects
// and methods like Promise.all([]) can only be done with promises

const myFetch1 = () => {
	return new Promise((resolve, reject) => {
		setTimeout(() => {
			if (Math.random() > 0.05) { // change this to trigger the catch blocks
				resolve('foo')
			} else {
				reject('Something went wrong')
			}
		}, 2000)
	})
}

const myFetch2 = () => {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
  		if (Math.random() > 0.15) {
       		resolve('bar')
      	} else {
        	reject('Something went wrong')
    	}
  	}, 3000)
  })
}

function getPromiseFoobar(cb) {
	const errCB = (err) => console.error(`something went wrong in getPromiseFoobar: ${err}`)
	myFetch1().then(val1 => {
		myFetch2().then(val2 => {
			cb(val1 + val2)
		}).catch(errCB)
	}).catch(errCB)
}

function getPromiseAllFoobar(cb) {
	Promise.all([myFetch1(), myFetch2()])
		.then(([a, b]) => cb(a + b))
		.catch((err) => console.error(`something went wrong in getPromiseAllFoobar: ${err}`))
}

async function getFoobar(cb) {
	try {
		const a = await myFetch1()
		const b = await myFetch2()
		cb(a + b)
	} catch(err) {
		console.error(`something went wrong in getFoobar: ${err}`)
	}
}

function main() {
	getFoobar(foobar => console.log('async await: ', foobar))
	getPromiseFoobar(foobar => console.log('promise: ', foobar))
	getPromiseAllFoobar(foobar => console.log('promise all: ', foobar))
}

main()