AngularJS – why is $apply required to properly resolve a $q promise?

In AngularJS the results of resolve() are propagated asynchronously, inside a $digest cycle, not immediately. This means that callbacks registered with then() will only be called (later) when a digest cycle occurs.

In your code, nothing is causing Angular to enter a digest cycle, so the then() callback is never called. Calling $apply() is one way to cause a digest cycle to run. Another way: add a button with ng-click that does nothing, then click that, it will cause a digest cycle and you should see the results:

<button ng-click="">Force digest by clicking me</button>

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