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

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.

Answer 2

Another reason to use $state.params is for non-URL based state, which (to my mind) is woefully underdocumented and very powerful.
I just discovered this while googling about how to pass state without having to expose it in the URL and answered a question elsewhere on SO.
Basically, it allows this sort of syntax:
<a ui-sref="toState(thingy)" class="list-group-item" ng-repeat="thingy in thingies">{{ thingy.referer }}</a>

Answer 3

EDIT: This answer is correct for version 0.2.10. As #Alexander Vasilyev pointed out it doesn't work in version 0.2.14.
Another reason to use $state.params is when you need to extract query parameters like this:
$stateProvider.state('a', {
url: 'path/:id/:anotherParam/?yetAnotherParam',
controller: 'ACtrl',
});
module.controller('ACtrl', function($stateParams, $state) {
$state.params; // has id, anotherParam, and yetAnotherParam
$stateParams; // has id and anotherParam
}

Answer 4

There are many differences between these two. But while working practically I have found that using $state.params better. When you use more and more parameters this might be confusing to maintain in $stateParams. where if we use multiple params which are not URL param $state is very useful
.state('shopping-request', {
url: '/shopping-request/{cartId}',
data: {requireLogin: true},
params : {role: null},
views: {
'': {templateUrl: 'views/templates/main.tpl.html', controller: "ShoppingRequestCtrl"},
'body#shopping-request': {templateUrl: 'views/shops/shopping-request.html'},
'footer#shopping-request': {templateUrl: 'views/templates/footer.tpl.html'},
'header#shopping-request': {templateUrl: 'views/templates/header.tpl.html'}
}
})

Answer 5

I have a root state which resolves sth. Passing $state as a resolve parameter won't guarantee the availability for $state.params. But using $stateParams will.
var rootState = {
name: 'root',
url: '/:stubCompanyId',
abstract: true,
...
};
// case 1:
rootState.resolve = {
authInit: ['AuthenticationService', '$state', function (AuthenticationService, $state) {
console.log('rootState.resolve', $state.params);
return AuthenticationService.init($state.params);
}]
};
// output:
// rootState.resolve Object {}
// case 2:
rootState.resolve = {
authInit: ['AuthenticationService', '$stateParams', function (AuthenticationService, $stateParams) {
console.log('rootState.resolve', $stateParams);
return AuthenticationService.init($stateParams);
}]
};
// output:
// rootState.resolve Object {stubCompanyId:...}
Using "angular": "~1.4.0", "angular-ui-router": "~0.2.15"

Answer 6

An interesting observation I made while passing previous state params from one route to another is that $stateParams gets hoisted and overwrites the previous route's state params that were passed with the current state params, but using $state.params doesn't.
When using $stateParams:
var stateParams = {};
stateParams.nextParams = $stateParams; //{item_id:123}
stateParams.next = $state.current.name;
$state.go('app.login', stateParams);
//$stateParams.nextParams on app.login is now:
//{next:'app.details', nextParams:{next:'app.details'}}
When using $state.params:
var stateParams = {};
stateParams.nextParams = $state.params; //{item_id:123}
stateParams.next = $state.current.name;
$state.go('app.login', stateParams);
//$stateParams.nextParams on app.login is now:
//{next:'app.details', nextParams:{item_id:123}}

Answer 7

Here in this article is clearly explained: The $state service provides a number of useful methods for manipulating the state as well as pertinent data on the current state. The current state parameters are accessible on the $state service at the params key. The $stateParams service returns this very same object. Hence, the $stateParams service is strictly a convenience service to quickly access the params object on the $state service.
As such, no controller should ever inject both the $state service and its convenience service, $stateParams. If the $state is being injected just to access the current parameters, the controller should be rewritten to inject $stateParams instead.