When to use promise.all()?

Question

This is more of a conceptual question. I understand the Promise design pattern, but couldn\'t find a reliable source to answer my question about promise.all():<

Answer 1

I tend to use promise all for something like this:

myService.getUsers()
   .then(users => {
       this.users = users;

       var profileRequests = users.map(user => {
           return myService.getProfile(user.Id); // returns a promise
       });

       return Promise.all(profileRequests);
   })
   .then(userProfilesRequest => {
       // do something here with all the user profiles, like assign them back to the users.

       this.users.forEach((user, index) => {
           user.profile = userProfilesRequest[index];
       });
   });

Here, for each user we're going off and getting their profile. I don't want my promise chain to get out of hand now that i have x amount of promises to resolve.

So Promise.all() will basically aggregate all my promises back into one, and I can manage that through the next then. I can keep doing this for as long as a like, say for each profile I want to get related settings etc. etc. Each time I create tonnes more promises, I can aggregate them all back into one.