AngularJS 1.x custom filter can't be injected, unknown provider -

i'm trying create custom filter, when try inject controller, 'unknown provider' error. have checked , double checked references, can't see what's wrong.

i know file referenced in index.html correctly, loaded , can found inspector. code have:

in app.js:

angular.module('equiclass', ['equiclass.controllers',                          'equiclass.services',                          'ngroute']) .config(function ($routeprovider) { $routeprovider   .when('/courses', {     templateurl: 'views/courses.html',     controller: 'coursectrl'   // , other stuff routes });  angular.module('equiclass.controllers', ['equiclass.services', 'equiclass.filters']); angular.module('equiclass.services', []); angular.module('equiclass.filters', []); 

my filter:

angular.module('equiclass.filters')   .filter('testfilter', function() {     return function(input) {       return undefined;     }; }); 

and controller:

angular.module('equiclass.controllers')   .controller('coursectrl', function ($scope, testfilter) {    }); 

of course quite simplified, doesn't work, , can't see why. have made several services , work , play along nicely.

you don't need inject filter itself.

this code...

angular.module('equiclass.controllers')   .controller('coursectrl', function ($scope, testfilter) {    }); 

should

angular.module('equiclass.controllers')   .controller('coursectrl', function ($scope) {    }); 

and inside coursectrl should use filter do.

injecting module 'equiclass.filters' module 'equiclass.controllers' enough.

i had similar issue , made post on blog.

--edit

as n00dl3 mentions below tricky part how auto-naming convention works in angular. if name filter specialnumberfilter when inject need refer specialnumberfilterfilter. allows use filter function, is.

// in controller vm.data = specialnumberfilterfilter(vm.data, 'a');

but believe can use filter without injecting controller if used in string expression being evaluated by, say, watch because same scenario when using in template.

// inside watch - no controller injection required `$scope.$watch('vm.data | specialnumberfilter', function(new, old) { ... })`