Promises and Async Await

	/*** Event Loop ***/
	// More priority for the promises over the setTimeOut and other ajax calls
	// Promises will be added to a seperate queue having more priority than callback.
	// Callbacks will be in a different queue in background which will be executed after the promises
	console.log('STARTS');
	setTimeout(() => console.log('0 secs timer.'), 0);
	Promise.resolve('Promise Resolve 1').then(response => {
	for(let i = 0; i < 40000000; i++) {}
	console.log(response)
	});
	Promise.resolve('Promise Resolve 2').then(response => console.log(response));
	console.log('ENDS');
	// First promise will execute and later setTimeOut due to priority
	/*** Developing a Promise ***/
	const examResultPromise = new Promise(function(resolve, reject) {
	console.log('Exam evaluation begins.');
	setTimeout(function() {
	if(Math.random() >= 0.5) {
	resolve('You are passed, Congratulations!!!');
	}
	else {
	reject(new Error('You are failed, Sorry!!!'));
	}
	}, 3000)
	});
	examResultPromise.then(res => console.log(res)).catch(err => console.error(err))
	/*** Promisifying setTimeOut ***/
	const wait = function(seconds) {
	return new Promise(function(resolve) {
	setTimeout(resolve, seconds * 1000);
	});
	};
	wait(2).then(() => {
	console.log('Waited for 2 seconds.')
	return wait(1);
	})
	.then(() => console.log('Waited for 1 second'));
	/*** Async - Await instead of promise ***/
	const getCountriesInfo = async function(country) {
	// fetch(`https://restcountries.com/v3.1/name/${country}`).then(res => console.log(res))
	const res = await fetch(`https://restcountries.com/v3.1/name/${country}`)
	console.log(res);
	const data = await res.json();
	console.log(data);
	return data[0].capital[0];
	};
	getCountriesInfo('india');
	/*** Error handling with try and catch ***/
	try {
	const myConst = 90;
	myConst = 100;
	}
	catch(error) {
	console.error(`*** ${error.message}`);
	}
	/*** Async functions returning a value ***/
	//getCountriesInfo('australia')
	//.then(res => console.log(res));
	// without Async, Await cannot be used
	// Using IIFE
	(async function() {
	const testVal = await getCountriesInfo('australia');
	console.log(testVal)
	})();
	/*** Calling promises in parallel ***/
	const get2Countries = async function(c1, c2) {
	const country1 = await getCountriesInfo(c1);
	// 2nd one will be called after the first one
	const country2 = await getCountriesInfo(c2);
	console.log(country1, country2);
	// To call all promises together
	const countries = await Promise.all([
	getCountriesInfo(c1),
	getCountriesInfo(c2)
	]);
	console.log(countries);
	};
	get2Countries('australia', 'canada');
	/***
	Promise: race - Which is fulfilled first either resolved or rejected
	***/
	// Promise.race for resolve
	(async function() {
	const res = await Promise.race([
	getCountriesInfo('india'),
	getCountriesInfo('canada'),
	getCountriesInfo('usa')
	]);
	console.log(res);
	})();
	// Promise.race for reject
	Promise.race([
	getCountriesInfo('india'),
	wait(0.2)
	])
	.then(() => console.log('Waited for sometime....'))
	.catch(err => console.log(err));
	// Promise.allSettled - Gives response of all the promises
	Promise.allSettled([
	Promise.resolve('Success'),
	Promise.reject('Error'),
	Promise.resolve('Success 2')
	])
	.then(res => console.log(res))
	.catch(error => console.error(error));
	// Promise.all - Gives first rejected promise
	Promise.all([
	Promise.resolve('Success'),
	Promise.reject('Error'),
	Promise.resolve('Success 2')
	])
	.then(res => console.log(res))
	.catch(error => console.error(error))
	// Promise.any - Gives first resolved promise
	Promise.any([
	Promise.resolve('Success'),
	Promise.reject('Error'),
	Promise.resolve('Success 2')
	])
	.then(res => console.log(res))
	.catch(error => console.error(error))

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