[AngularJS] Decorator pattern for code reuse

Imaging you have a large application, inside this large application you have many small individual applications.

                 main app

          /             |               \

    small A     Small B     Small C

 

For example you are building a redirection service in main app, you want to share some common partten code with small apps A,B,C.

There is one function inside redirection servcice:

Class RedirectionService {
  getUrl ({state, isCustomer, namespace}) {

  }
}

It takes one object which contains 'state', which means in different state, we should redirection to different URL. 

Second params is 'isCustomer', which tell whether current user is onboarded customer or not.

Last is 'namespace', which refer to Small A or Small B or Small C applications. Those applications have differnet url configed.

 

Now the problem is everytime from Small application, I have to tell all three params in order to make it works:

// small A
RedirectService.getUrl ({state: 'some state', isCustomer: CustomerA.isCustomer, namespace: 'small_A'})
RedirectService.getUrl ({state: 'some state_a2', isCustomer: CustomerA.isCustomer, namespace: 'small_A'})

// small B
RedirectService.getUrl ({state: 'some state_b1', isCustomer: CustomerB.isCustomer, namespace: 'small_B'})
RedirectService.getUrl ({state: 'some state_b2', isCustomer: CustomerB.isCustomer, namespace: 'small_B'})

 

So what we actually prefer is calling like this:

// Small A
RedirectService.getUrl('some state_a1')

// Small B
RedirectService.getUrl('some state_b1')

From small applciation component level, we only care 'state',  we don't want to take care 'isCustomer' or 'namespace'.

 

To achieve this, we can use 'decorator' it is great way to code reuse.

// Take care isCustomer, by inject Customer service for based on different applications.
function NewRedirectionService($delegate, CustomerA) {
    // store original function from Redirection Service
    const getUrl = $delegate.getUrl;

    // Create a high order function to wrap original function
¨  // for small apps, they will call this new function instead
    function newGetUrl(state) {
        // apply common params and call original function
        return getUrl.call($delegate, {state, isCustomer: CustomerA.isCustomer, namespace: 'small_A'});
    }

    // override original function by new function.
    $delegate.getUrl = newGetUrl;

    return $delegate;
}

// Re-declare 'RedirectService' by using 'decorator'
angular.module('shared').decorator('RedirectionService', NewRedirectionService);

 

As you can see now, from compmonent level, 

before:

RedirectService.getUrl ({state: 'some state', isCustomer: CustomerA.isCustomer, namespace: 'small_A'})

now:

RedirectService.getUrl ('some state')