PromiseLearning

/**
 * resolving promise
 */
let p = new Promise((resolve, reject) => resolve('resolved'))

/**
 * rejecting promise
 * 
 * comment out when not using to prevent errors
 */
let pFail = new Promise((resolve, reject) => reject('rejected'))

/**
 * random rejection promise
 */
let randomP1 = new Promise((resolve, reject) => {
    let r = Math.random()
    if (r > .25 && r < .75) {
        reject('rejection: Math.random() was between .25 and .75');
    } else {
        setTimeout(resolve('resolved'), 1000)
    }
})
let randomP2 = new Promise((resolve, reject) => {
    let r = Math.random()
    if (r > .25 && r < .75) {
        reject('rejection: Math.random() was between .25 and .75');
    } else {
        setTimeout(resolve('resolved'), 1000)
    }
})
let randomP3 = new Promise((resolve, reject) => {
    let r = Math.random()
    if (r > .25 && r < .75) {
        reject('rejection: Math.random() was between .25 and .75');
    } else {
        setTimeout(resolve('resolved'), 1000)
    }
})

// arrays to pass to Promise.all()
let promises = [ p, p, p ];
let promisesWithFail = [ pFail, p, p, p ];
let promiseswithRandom = [ pFail, randomP1, randomP2, randomP3 ];

/**
 * all promises in series
 */

const allInSeries = async () => {
    Promise.all(promises)
    .then(results => {
        for (let i = 0; i < results.length; ++i) {
            console.log(`results[i], promise.all => `, results[i]);
        }
    }).catch(err => console.error(err))
}
// allInSeries();

/**
 * all promises regardless of error
 */
let allPromises = async () => {
    let results = [];
    let _p = null;
    for (let i = 0; i < promisesWithFail.length; ++i) {
        try {
            _p = await promisesWithFail[i];
            results.push(_p)
        } catch(err) {
            results.push(err);
        }
    }
    console.log('all with potential fail => ', results);
}
// allPromises();

/**
 * first promise fulfilled
 */
const firstWithPotentialFail = async() => {
    let results = [];
    let _p = null;
    for (let i = 0; i < promisesWithRandom.length; ++i) {
        try {
            if (results.length > 0) {
                continue;
            } else {
                _p = await promisesWithRandom[i];
                results.push(_p)
            }
        } catch(err) {
            console.error('rejection => ', err)
        }
    }
    console.log('first resolved promise => ', results);
}
// firstWithPotentialFail()