System.import promise chaining

Question

I've stumbled upon some snippets similar to this one:

  System.import('core-js').then( function() {
    System.import('polymer/mutationobservers').then( function() {
      System.import('aurelia-bootstrapper');
    })
  });

Is it a substitution for callback hell - a promise hell? Can sequential System.imports be flattened to make use of promise chaining, or there may be problems with that?

Answer 1

I'd recommend chaining instead, e.g.

System.import('core-js')
    .then(function(){
        return System.import('polymer/mutationobservers');
    })
    .then(function(){
        return System.import('aurelia-bootstrapper');
    });

When you return a promise from a then, it will wait for that to resolve before executing the next then, so in this case mutationobservers must load before aurelia-bootstrapper.