Angular's $q promises provide a powerful abstraction over flow control - see [the official documentation](https://docs.angularjs.org/api/ng/service/$q). If you tag your question with this tag consider also tagging it with [tag:promise]. This tag is also appropriate for questions about angular and promises not relaying to $q directly.

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The idea is simple enough – you want to create a service that captures the data and stores is and then notify the controller that the data has changed or refreshed. Let’s look at a few different approaches to help us understand how the $http service works with its custom promises.