Modern APIs are often realized in a RESTful way. Besides being stateless and using the correct HTTP verbs for specific actions, REST does not specify the response of a request. Hypermedia Formats are trying to overcome this issue by providing a discoverable API. Hypermedia Application Language is one format and abbreviates as HAL.
HAL is a set of conventions expressing hyperlinks in either JSON or XML. Resources returned by a HAL API contain a _links element hosting a self link and a link to resources. This makes HAL APIs discoverable as it is possible to navigate from one resource to another via the links provided within the resources knowing only a single entry point. This article describes how to use HAL hypermedia APIs in Angular.