Simple Asynchronous JavaScript Promise Example

javascript-promise-examples.js

// TODO
// Add Promise.race example
// Add Promise.all example
// Refactor async simulations to better reflect real-world scenarios
// Refactor so that if the evenOrOdd async work is not wrapped in a Promise that it could cause unexpected behavior sometimes depending on JS Type/Reference errors
function getRandomData() {
    return {
        number: Math.floor(Math.random() * 10),
        timeout: Math.floor(Math.random() * 10000)
    }
}

function evenOrOdd(data) {
    return new Promise(function(resolve, reject) { // Wrapping reponse in Promise to ensure explicit Promise behavior regardless of data
        setTimeout(function() { // Simulate another async request in the Promise then chain
            if (!(data.number % 2)) {
                resolve(`The count was even, I resolved with: [${data.number}] it took ${data.timeout + 1000} milliseconds`);
            }
            else {
                reject(`The count was odd, I resolved with: ${data.number} it took ${data.timeout + 1000} milliseconds`);
            }
        }, data.timeout);
    });
}

function onFulfilled(data) {
    console.log('onFulfilled Called');
    console.log('.......do fulfilling things.......')
    console.log(data);
}

function onRejected(reason) {
    console.log('onRejected Called');
    console.log('Rejected reason:', reason);
    console.log('.......do error handling things.......')
}

var asyncRequest = new Promise (function(resolve, reject) {
    setTimeout(function() { // Simulating asynchronous event like an AJAX call
        resolve(getRandomData());
    }, 1000);
});

asyncRequest
    .then(evenOrOdd)
    .then(onFulfilled)
    .catch(onRejected);

/* Resources
    https://github.com/getify/You-Dont-Know-JS/blob/master/async%20%26%20performance/ch3.md#chapter-3-promises
    http://www.ecma-international.org/ecma-262/6.0/#sec-promise-constructor
    https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise
*/