angularjs - `ui-router` $stateParams vs. $state.params

Question

With ui-router, it's possible to inject either $state or $stateParams into a controller to get access to parameters in the URL. However, accessing parameters through $stateParams only exposes parameters belonging to the state managed by the controller that accesses it, and its parent states, while $state.params has all parameters, including those in any child states.

Given the following code, if we directly load the URL http://path/1/paramA/paramB, this is how it goes when the controllers load:

$stateProvider.state('a', {
     url: 'path/:id/:anotherParam/',
     controller: 'ACtrl',
  });

$stateProvider.state('a.b', {
     url: '/:yetAnotherParam',
     controller: 'ABCtrl',
  });

module.controller('ACtrl', function($stateParams, $state) {
   $state.params; // has id, anotherParam, and yetAnotherParam
   $stateParams;  // has id and anotherParam
}

module.controller('ABCtrl', function($stateParams, $state) {
   $state.params; // has id, anotherParam, and yetAnotherParam
   $stateParams;  // has id, anotherParam, and yetAnotherParam
}

The question is, why the difference? And are there best practices guidelines around when and why you should use, or avoid using either of them?

Answer 1

The documentation reiterates your findings here: https://github.com/angular-ui/ui-router/wiki/URL-Routing#stateparams-service

If my memory serves, $stateParams was introduced later than the original $state.params, and seems to be a simple helper injector to avoid continuously writing $state.params.

I doubt there are any best practice guidelines, but context wins out for me. If you simply want access to the params received into the url, then use $stateParams. If you want to know something more complex about the state itself, use $state.