Demonstrating different ways of using promises with(out) async/await that are dependent on multiple promises

promise_variations.js

const sleep=(fn,ms)=>new Promise(r=>setTimeout(()=>r(fn()),ms));
const init=Date.now();
const log=(y)=>console.log((Date.now()-init)+' '+y);

//7: Awaiting on required values immediately. Very slow.
(async () => {
	const x=await sleep(()=>1,100);
	const a=await sleep(()=>3,200);
	const b=await sleep(()=>4,300);

	const ax=await sleep(()=>a*x**2,1000);
	const bx=await sleep(()=>b*x,500);

	return ax + bx;
})().then(log);

/*20: Initialize promises, then await. This is faster, but ax_p can't run until
  b_p resolves. We could await b_p after ax_p because ax_p doesn't need b_p and
  we know b_p will take longer to resolve since we can see the timings, but in
  real world scenarios, timings are unpredictable.*/
(async () => {
	const x_p=sleep(()=>2,100);
	const a_p=sleep(()=>3,200);
	const b_p=sleep(()=>4,300);

	const x=await x_p;
	const a=await a_p;
	const b=await b_p;

	const ax_p=sleep(()=>a*x**2,1000);
	const bx_p=sleep(()=>b*x,500);

	return await ax_p + await bx_p;
})().then(log);

//39: Same as before, but with Promise.all().
(async () => {
	const x_p=sleep(()=>3,100);
	const a_p=sleep(()=>3,200);
	const b_p=sleep(()=>4,300);

	const [x,a,b]=await Promise.all([x_p,a_p,b_p]);
	const [ax,bx]=await Promise.all([
		sleep(()=>a*x**2,1000),
		sleep(()=>b*x,500)
	]);

	return ax + bx;
})().then(log);

//64: Use nested async/await to only await the values needed for each result.
(async () => {
	const x_p=sleep(()=>4,100);
	const a_p=sleep(()=>3,200);
	const b_p=sleep(()=>4,300);

	const ax_p=(async ()=>{
		const a=await a_p;
		const x=await x_p;
		return await sleep(()=>a*x**2,1000);
	})();
	const bx_p=(async ()=>{
		const b=await b_p;
		const x=await x_p;
		return await sleep(()=>b*x,500);
	})();

	return await ax_p + await bx_p;
})().then(log);

//95: Same as before, but with Promise.all().
(async () => {
	const x_p=sleep(()=>5,100);
	const a_p=sleep(()=>3,200);
	const b_p=sleep(()=>4,300);

	const [ax,bx]=await Promise.all([
		(async ()=>{
			const [a,x]=await Promise.all([a_p,x_p]);
			return await sleep(()=>a*x**2,1000);
		})(),
		(async ()=>{
			const [b,x]=await Promise.all([b_p,x_p]);
			return await sleep(()=>b*x,500);
		})()
	]);

	return ax + bx;
})().then(log);

//132: Same as before, but without any async/await, just raw promises.
(() => {
	const x_p=sleep(()=>6,100);
	const a_p=sleep(()=>3,200);
	const b_p=sleep(()=>4,300);

	const ax_p=Promise.all([a_p,x_p]).then(([a,x])=>sleep(()=>a*x**2,1000));
	const bx_p=Promise.all([b_p,x_p]).then(([b,x])=>sleep(()=>b*x,500));

	return Promise.all([ax_p,bx_p]).then(([ax,bx])=>ax+bx);
})().then(log);

/*
End result:
1203 132
1205 64
1205 95
1304 20
1304 39
2104 7
*/