Sequential promise loop with delay

Question

I\'m attempting to load an array of \"requests\" sequentially each one separated by a delay.

I\'m using promises but for some reasons I\'m having issues with the req

Answer 1

The issue is that you're not updating sequence to include any of the successive operations, so all of them are chaining off of that original resolved promise. There's nothing there to delay any of them, so they execute right away.

You should be able to remedy this simply by updating the sequence variable on every loop, so you're chaining off the end of the chain:

//object I need to use to construct requests
var batches = [of_objects];
var sequence = Promise.resolve();
var self = this;

batches.forEach(function (batch){
    sequence = sequence            // <-- here
        //Function returns promise
        .then( function(){
            return self._createRequestPromise(batch); //this runs first 5x
        })
        //callback so we can update, returns nothing
        .then(callback)
        //add 3 sec timeout before next request
        .then(function(){
            return new Promise(function (resolve, reject){
                setTimeout(resolve, 3000); //this runs after 5x
            });
        });
});

return sequence;

Personally, I try to avoid overwriting variables, so an alternate way to do this without variable reassignment is to use .reduce():

//object I need to use to construct requests
var batches = [of_objects];
var self = this;

return batches.reduce(function (last, batch){
    return last
        //Function returns promise
        .then( function(){
            return self._createRequestPromise(batch); //this runs first 5x
        })
        //callback so we can update, returns nothing
        .then(callback)
        //add 3 sec timeout before next request
        .then(function(){
            return new Promise(function (resolve, reject){
                setTimeout(resolve, 3000); //this runs after 5x
            });
        });
}, Promise.resolve());