[Best]RunPromisesSequentially.js

var timer = (ms) => {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            resolve();
        }, ms)
    });
}

promises = [timer(3000), timer(5000), timer(1000), timer(2000)]
promises.reduce((chain, promise, idx) => {
    console.log('Begin loop', idx)
    return chain
        .then(() => {
            console.log('Return promise', idx)
            return promise
        })
        .then(() => {
            console.log('Result', idx)
        })
}, Promise.resolve())


// Same result:
Promise.resolve()
    .then(() => {
        console.log('Return promise', 0)
        return promises[0]
    })
    .then(() => {
        console.log('Result', 0)
        console.log()
    })
    .then(() => {
        console.log('Return promise', 1)
        return promises[1]
    })
    .then(() => {
        console.log('Result', 1)
        console.log()
    })
    .then(() => {
        console.log('Return promise', 2)
        return promises[2]
    })
    .then(() => {
        console.log('Result', 2)
        console.log()
    })
    .then(() => {
        console.log('Return promise', 3)
        return promises[3]
    })
    .then(() => {
        console.log('Result', 3)
        console.log()
    })