Create a Promise Chain for Request Handling with Delays

Question

I want to create a chain of requests that get data from a server, but between each request a delay of X seconds should happen.

Should go like this:

const data = {};
const promises = Promise.resolve();
for (let elem of longArray) {
    promises.then(() => {
        return sendRequest(); // returns promise
    })
    .then((response) => {
        // Store response stuff in data
    })
    .then(() => {
        // Wait here for X seconds before continuing
    })
}

promises.finally(() => {
    // Log stuff from data
});

However, I don't get it doing what I want. It immediately fires all requests and then goes in the response handler. And the finally part is called before the data was filled.

Answer 1

As you are using bluebird, it's very simple using array.reduce

const data = {};
longArray.reduce((promise, item) => 
    promise
        .then(() => sendRequest())
        .then(response => {
            // Store response stuff in data
        }).delay(X), Promise.resolve())
.finally(() => {
    // Log stuff from data
});

or - using your for...of loop

const data = {};
const promises = Promise.resolve();
for (let elem of longArray) {
    promises = promises
    .then(() => sendRequest())
    .then(response => {
        // Store response stuff in data
    })
    .delay(X);
}

promises.finally(() => {
    // Log stuff from data
});