[$injector:unpr] Unknown provider: myServiceProvider <- myService

The [$injector:unpr] Unknown Provider error occurs in AngularJS when Angular cannot find or inject a dependency (service, factory, provider, etc.) into a component. This typically happens due to issues in dependency injection (DI).

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1. Understanding [$injector:unpr] Error

Error Message in Console:

Error: [$injector:unpr] Unknown provider: myServiceProvider <- myService

What This Means:

• AngularJS is trying to inject myService, but it cannot find myServiceProvider.
• This usually happens when:
  • myService is not defined.
  • The service is not registered properly.
  • A misspelling in service name or dependency injection syntax.

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2. Common Causes & Fixes

1. Service is Not Defined Before Usage

Issue:
If myService is not properly defined before using it, AngularJS cannot inject it.

Incorrect Code:

angular.module('myApp', [])
  .controller('MyController', function(myService) { // myService is not defined yet
      myService.doSomething();
  });

Fix:
Define myService before using it:

angular.module('myApp', [])
  .service('myService', function() {
      this.doSomething = function() {
          console.log('Service is working!');
      };
  })
  .controller('MyController', function(myService) { // Now it is defined
      myService.doSomething();
  });

---

2. Service is Not Registered in the Correct Module

Issue:
If myService is defined in a different module that is not injected into myApp, AngularJS won’t recognize it.

Incorrect Code (Module Not Injected):

angular.module('serviceModule', [])
  .service('myService', function() {
      this.doSomething = function() {
          console.log('Service is working!');
      };
  });

angular.module('myApp', []) // 'serviceModule' is missing here
  .controller('MyController', function(myService) { 
      myService.doSomething();
  });

Fix:
Inject the correct module into myApp:

angular.module('serviceModule', [])
  .service('myService', function() {
      this.doSomething = function() {
          console.log('Service is working!');
      };
  });

angular.module('myApp', ['serviceModule']) // Include 'serviceModule'
  .controller('MyController', function(myService) { 
      myService.doSomething();
  });

---

3. Misspelling the Service Name

Issue:
AngularJS is case-sensitive. If there is a typo in the service name, Angular won’t find it.

Incorrect Code (Spelling Mistake):

angular.module('myApp', [])
  .service('MyService', function() { // Capital 'M'
      this.doSomething = function() {
          console.log('Service is working!');
      };
  })
  .controller('MyController', function(myservice) { // Lowercase 'm'
      myservice.doSomething(); // Error!
  });

Fix:
Use consistent spelling and casing:

angular.module('myApp', [])
  .service('myService', function() { 
      this.doSomething = function() {
          console.log('Service is working!');
      };
  })
  .controller('MyController', function(myService) { // Match the correct case
      myService.doSomething();
  });

---

4. Incorrect Dependency Injection in Minified Code

Issue:
AngularJS relies on function parameter names for DI. When minified, parameter names change, breaking DI.

Incorrect Code:

angular.module('myApp', [])
  .service('myService', function() { 
      this.doSomething = function() {};
  })
  .controller('MyController', function(myService) { 
      myService.doSomething();
  });

When Minified, it Becomes:

.controller('MyController', function(a) { // 'myService' becomes 'a', breaking DI
    a.doSomething();
});

Fix: Use array-style injection to prevent this issue:

angular.module('myApp', [])
  .service('myService', function() { 
      this.doSomething = function() {};
  })
  .controller('MyController', ['myService', function(myService) { 
      myService.doSomething();
  }]);

---

5. Using provider Instead of service or factory Incorrectly

Issue:
Providers in AngularJS need an explicit .get() method when being injected.

Incorrect Code:

angular.module('myApp', [])
  .provider('myService', function() {
      this.doSomething = function() {
          console.log('This will not work!');
      };
  })
  .controller('MyController', function(myService) { // Error!
      myService.doSomething();
  });

Fix:
Use .get() inside $get when defining a provider:

angular.module('myApp', [])
  .provider('myService', function() {
      this.$get = function() {
          return {
              doSomething: function() {
                  console.log('Now it works!');
              }
          };
      };
  })
  .controller('MyController', function(myService) {
      myService.doSomething();
  });

If you don’t need advanced configurations, use service or factory instead of provider.

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6. Factory/Service Not Returning an Object

Issue:
Factories and services must return an object or function for dependency injection to work.

Incorrect Code (No Return Statement in Factory):

angular.module('myApp', [])
  .factory('myService', function() {
      var data = "This will not work!";
  })
  .controller('MyController', function(myService) { 
      console.log(myService); // Undefined
  });

Fix:
Ensure the factory returns an object:

angular.module('myApp', [])
  .factory('myService', function() {
      return {
          data: "Now it works!"
      };
  })
  .controller('MyController', function(myService) { 
      console.log(myService.data); // Outputs: "Now it works!"
  });

---

3. Debugging Steps in Chrome DevTools

Step 1: Check the Console for Errors

• Open Developer Tools (F12) → Go to Console
• Look for [$injector:unpr] errors and identify the missing service

Step 2: Manually Check if the Service is Registered Run this in the browser console:

angular.module('myApp')._invokeQueue

• Look for myService in the output. If missing, the module might not be loaded.

Step 3: Verify Script Load Order

• Open the Network tab and check if all required JavaScript files are loaded.

Step 4: Check the Dependency Injection Syntax

• Use array-style injection (['myService', function(myService) { ... }]) to avoid minification issues.