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function allSequential(promiseFns) {
    const initPromise = Promise.resolve([]);
    return promiseFns.reduce(_chainPromise, initPromise);
 
    function _chainPromise(acc, pFn) {
        return acc.then(result => pFn().then(pResult => [...result, pResult]));
    }
}
 
allSequential([

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return Promise.all([
    task1(),
    task2(),
    task3()
]).then(([r1,r2,r3]) => {
    // every promise was fulfilled
    // do work with r1, r2 and r3
    // results are granted to be sorted as received
})
.catch(err => {

nsacerdote

function doSomething() {
    const results = {};
    return performStep1()
        .then(result1 => (results.one = result1))
        .then(() => performStep2(results.one))
        .then(result2 => (results.two = result2))
        .then(() => performStep3(results.two))
        .then(result3 => performFinalStep(results.one, result3))
        .then(finalResult => ({
            result2: results.two,

nsacerdote

function doSomething() {
    return performStep1()
        .then(result1 => performStep2(result1))
        .then(result2 => performStep3(result2))
        .then(result3 => performFinalStep(result3));
}

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function doSomething() {
    return performStep1().then(result1 =>
        performStep2(result1).then(result2 =>
            performStep3(result2).then(result3 =>
                performFinalStep(result3)
            )
        )
    );
}

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function wrapper() {
    return new Promise((resolve, reject) => {
        doNodeStuff((error, result) => {
            if (error) {
                reject(error);
            } else {
                resolve(result);
            }
        });
    });

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function doSomething(input) {
    if (!input) {
        return Promise.reject('missing input'); // returns a rejected promise
    } else {
        return Promise.resolve(input + ' done'); // returns a fulfilled promise
    }
}

nsacerdote

function doSomething(input) {
    return new Promise((resolve, reject) => {
        if (!input) {
            reject('missing input');
        } else {
            resolve(input + ' done');
        }
    });
}

nsacerdote

function doSomething() {
    return fetch('http://example.com/movies.json')
        .then(response => response.json());
}

nsacerdote

function doSomething() {
    return new Promise((resolve, reject) => {
        fetch('http://example.com/movies.json')
            .then(response => resolve(response.json()))
            .catch(err => reject(err));
    });
}