---

title: Hook sidebar_label: Hook

Hook is the mechanism allowing a specific host to define what (and how) can be extended.

Available hooks are defined as part of capacities by maps detailing properties and their associated type. They leverage references to use various extensions elements.

{:capacities {hooks/main.my-hook {:properties {:view :view :name :string}}}}

Properties are defined as map of property name (keyword) / property types.

Type can be:

• :string, :keyword
• references to :view, :event or :query
• one of a set: {:one-of #{:one :two}}
• subset of: #{:one :two :three}
• complex types {:child {:name :string}} and {:children [{:name :string}]}

Extensions can then specify hooks that will match associated host capacities. Hooks implemented by extensions must be qualified with an extra id. This id will be globally unique across all extensions per hook. e.g. an extension implementing hooks/main could define a hook with id hooks/main.demo.

A hook is defined by a map that consists of a number of pairs specific to each extension type. As shown below, the hooks/main.demo hook requires two additional keys: name and view.

{meta
 {:name ""
  ...}
 
 views/main
 [text {}
  ""]

 hooks/main.demo
 {:view @views/main
  :name "test"}}

Once a host has loaded a valid extension with matching hooks, it can query the resulting map.

References

Views

Views references are resolved as a function of one argument that returns hiccup data. The argument must be a map of key/value pairs. This map is used as value for properties reference available in let blocks.