javascript-with-promises-async.js

/*
var async = true;
var xhr = new XMLHttpRequest();
xhr.open('get', 'favicon.ico', async);
xhr.send();

var timestamp = Date.now() + 3000;

while(Date.now() < timestamp);

function listener(msg) {
    console.log('Greetings from listner ', msg);
}

xhr.addEventListener('error', listener);
xhr.addEventListener('load', listener);
*/
// request
/*
function repositionElement() {
    console.log('repositioning..');
}

window.requestAnimationFrame(repositionElement);

console.log('I am the last line of the script');
*/
/*
var async = true;
var xhr = new XMLHttpRequest();
xhr.open('get', 'data.json', async);
xhr.send();
setTimeout(function delayed() {
    // Creates race condition!    
    function listener() {
        console.log('greetings from listener');
    }
    xhr.addEventListener('load', listener);
    xhr.addEventListener('error', listener);
}, 550);

*/
/* 
// loadImage, callback style
function loadImage(url, success, error) {
    var img = new Image();
    img.src = url;
    img.onload = function() {
        success(img);
    }
    ;
    img.onerror = function(e) {
        error(e);
    }
    ;
}

loadImage('http://omid.fi/wiki/lib/tpl/dokuwiki/images/logo.png', function onsuccess(img) {
    // Add the image to the current web page        
    document.body.appendChild(img);
}, function onerror(e) {
    console.log('Error occurred while loading image');
    console.log(e);
});
*/

/*
// loadImage promise style
function loadImage(url) {
    var promise = new Promise(function resolver(resolve, reject) {
        var img = new Image();
        img.src = url;
        img.onload = function() {
            resolve(img);
        }
        ;
        img.onerror = function(e) {
            reject(e);
        }
        ;
    }
    );
    return promise;
}
var wikiImage = 'https://www.safaribooksonline.com/library/view/javascript-with-promises/9781491930779/assets/jswp_0201.png';
loadImage(wikiImage).then(function(img) {
    document.body.appendChild(img);
    console.log('yes got added!')
}).catch(function(e) {
    console.log('error tuli!');
    console.log(e);
});

*/

// promise state is set only once!
/*
var promise = new Promise(function (resolve, reject) {
    resolve(Math.PI);
    reject(0);
    resolve(Math.sqrt(-1));
});


promise.then(function (number) {
    console.log('The number is ' + number);
});
*/

// Promise.resolve('some value') and Promise.reject('some reason') are
// shorthands to resolve / reject a promise quickly
/*
var promise = new Promise(function (resolve, reject) {
    resolve(Promise.resolve(Math.PI));
    reject(0);
    resolve(Math.sqrt(-1));
});


promise.then(function (number) {
    console.log('The number is ' + number);
});

new Promise(function (resolve, reject) {
    resolve ('the long way');
});
*/

// example 2-8 call to then always returns a new promise
/*
var p1, p2;

p1 = Promise.resolve();
p2 = p1.then(function() {});

console.log('p1 and p2 are different objects: ' + (p1 !== p2));

*/

// passing values in a sequence of steps
/*
Promise.resolve('tada!').then(
    function step2(result) {
        console.log('Step 2 received ' + result); 
        return 'Greetings from step 2';
    }
).then(
    function step3(result) {
        console.log('Step 3 recieved '+ result);

    }
).then(
    function step4(result) {
        console.log('step 4 recieved ' + result);
        return Promise.resolve('Fulfilled value');
    }
).then(
    function step5(result){
        console.log('step 5 recieved ' + result);
    }
);

*/


// execution order of callbacks used by promises
/*
var promise = new Promise(function (resolve, reject){
    console.log('Inside the resolver function');
    resolve();
});

promise.then(function () {
    console.log('Inside the onFulFilled handlre');
});

console.log('This is the last line of script');
*/

// Error handling
/*
Promise.reject(Error('bad news')).then(
    function step2() {
        console.log('This is never run');
    }
).then(
    function step3() {
        console.log('This is also never run ');
    }
).catch(
    function error(err) {
        console.log('something failed along the way, Inspect error for more info');
        console.log(err);
    }
);
*/

function rejectWith (val) {
    return new Promise(function (resolve, reject) {
        throw Error(val);
        resolve('Not used');
    });
}


rejectWith('bad news').then(
    function step2() {
        console.log('This is never run');
    }
).catch(
    function(error) {
        console.log('Failed again!');
        console.log(error);
    }
);