ember install ember-router-helpers
route-params
{{#let (route-params "parent.child") as |routeParams|}}
<a href={{routeParams.url}} class={{if routeParams.isActive "active" "inactive"}}>Blah</a>
{{/let}}
transition-to
<button {{on "click" (transition-to "parent.child")}}></button>
replace-with
<button onclick={{replace-with "parent.child"}}></button>
is-active
{{is-active "parent.child"}}
url-for
{{url-for "parent.child"}}