A quick script to play with Promise nesting and resolution (node index.js)

index.js

function buildPromise(tag, shouldError) {
    if (shouldError) {
        return new Promise((resolve, reject) => {
            console.log(tag + " executor")
            setTimeout(() => { console.log(tag + " rejecting!"); reject(tag + " failed on purpose") }, 250)
        })
    }

    return new Promise((resolve, reject) => {
        console.log(tag + " executor")
        setTimeout(() => { console.log(tag + " resolving!"); resolve(tag + " succeed on purpose") }, 250)
    })
}

// Play with the `false/true` values are different places which controls resolve/reject for each promise
// Play with then/catch structure and nesting to see how the various things connects together
buildPromise("top", false).then((result) => {
    console.log(result + " => then block")
    return Promise.all([buildPromise("then > child1", false), buildPromise("then > child2", true), buildPromise("then > child1", false)])
}).catch((error) => {
    console.log(error + " => catch block")
    return Promise.all([buildPromise("catch > child1", false), buildPromise("catch > child2", false), buildPromise("catch > child1", false)])
}).then((result) => {
    console.log("after top", result)
})

output.txt

$ node /tmp/promise-test.js
top executor
top resolving!
top succeed on purpose => then block
then > child1 executor
then > child2 executor
then > child1 executor
then > child1 resolving!
then > child2 rejecting!
then > child1 resolving!
then > child2 failed on purpose => catch block
catch > child1 executor
catch > child2 executor
catch > child1 executor
catch > child1 resolving!
catch > child2 resolving!
catch > child1 resolving!
after top [ 'catch > child1 succeed on purpose',
  'catch > child2 succeed on purpose',
  'catch > child1 succeed on purpose' ]