Promises Examples

app.js

const fs = require("fs")

fs.readFile('test.txt', 'utf-8', (err, contentFile) => {

	setTimeout( ()=> {

		contentFile = contentFile.toUpperCase();

		fs.writeFile('output.txt', contentFile, (err) => {
			console.log("file written")
		})

	}, 2000)

})

appPromised.js

const fs = require("fs")

var readFilePromised = function(fileToRead) {
	return new Promise( (resolve,reject) => {
		fs.readFile(fileToRead, 'utf-8', (err, contentFile) => {
			resolve(contentFile)
		})
	})
}

var delayedAction = function(contentFile) {
	return new Promise( (resolve,reject) => {
		setTimeout( ()=> {
			contentFile = contentFile.toUpperCase();
			resolve(contentFile)
		})
	})
}

var writeFilePromised = function(contentToWrite) {
	return new Promise( (resolve,reject) => {
		fs.writeFile('output.txt', contentToWrite, (err) => {
			resolve("file written!")
		})
	})
}

function shoutOut( content ) {
	console.log (content)
	return content;
}

readFilePromised('test.txt')
	.then( delayedAction )
	.then( shoutOut )
	.then( writeFilePromised )
	.then( console.log )

promisesExamples.js

var promise1 = new Promise(function (fulfill, reject) {
	var msg = "1st Promise Resolved..."
	setTimeout( function() { fulfill(msg)}, 3000)
});

var promise2 = new Promise(function (fulfill, reject) {
	var msg = "and 2nd Promise Resolved to..."
	setTimeout( function() { fulfill(msg)}, 5000)
});

var promise3 = new Promise(function (fulfill, reject) {
	var msg = "and 3rd Promise also Resolved!"
	setTimeout( function() { fulfill(msg)}, 10000)
});


// Your solution here

function showMsg (text) {
	console.log(text);
}

/* Way 1 - Callback Promises Hell */

// promise1.then( function( msg ) {
// 	showMsg(msg);
// 	promise2.then( function( msg ) {
// 		showMsg(msg);
// 		promise3.then( function( msg ) {
// 			showMsg(msg);
// 		});
// 	})
// })

/* Way 2 - Returning Promises */

// promise1
// 	.then( function(msg) {
// 		showMsg(msg);
// 		return promise2;
// 	})
// 	.then( function(msg) {
// 		showMsg(msg);
// 		return promise3;
// 	})
// 	.then( function(msg) {
// 		showMsg(msg);
// 	})

/* Way 3 - Inproving Returning Promises */

// function showMsgEnhanced (text) {
// 	console.log(text);
// 	return (text)
// }


// promise1
// 	.then( showMsgEnhanced )
// 	.then (function(msg) {
// 		console.log ("prev Msg => " + msg)
// 		return promise2
// 		  .then(showMsgEnhanced);
// 	})
// 	.then (function(msg) {
// 		console.log ("prev Msg => " + msg)
// 		return promise3
// 		  .then(showMsgEnhanced);
// 	})

/* Way 4 - Inproving Returning Promises */

function showMsgEnhanced (text) {
	console.log(text);
	return (text)
}

function showPrevMsgAndDoSomethingPromised2 (msg) {
	console.log ("prev Msg => " + msg)
	return promise2
}

function showPrevMsgAndDoSomethingPromised3 (msg) {
	console.log ("prev Msg => " + msg)
	return promise3
}

promise1
	.then( showMsgEnhanced )
	.then( showPrevMsgAndDoSomethingPromised2 )
	.then( showMsgEnhanced )
	.then( showPrevMsgAndDoSomethingPromised3 )
	.then( showMsgEnhanced );

promisesQ-AllExample.js

function getSearchData( arrayAPI ) {

		function createPromiseFromItem ( item ) {
			var getUrl = 'https://api.spotify.com/v1/search?q='+ item +'&type=track';
			return appFactory.apiResult( getUrl ); // returns a promise
		}

		function showConsole(data) {
			console.log(data);
		}
		// ["aaaa", "vbbbbb", "cccccc"]
		// [Promise, Promise, Promise ]

		$q.all( arrayAPI.map(createPromiseFromItem) )
			.then( showConsole );

}

promisesRaceAll.js

var promise = new Promise(function(resolve, reject) {
  setTimeout(function() {
    resolve("operation completed!!")
  },5000)
});

var promise2 = new Promise(function(resolve, reject) {
  setTimeout(function() {
    resolve("another operation completed!!")
  },3000)
});

var allPromise = Promise.all([promise, promise2]);
var racePromise = Promise.race([promise, promise2]);

allPromise.then(function(data) {
  console.log( data )
})

racePromise.then(function(data) {
  console.log( data )
})