Using 'this' inside angularjs service

I would like to know whether the following code is bad practice. (This code is a angularjs service def)

**NOTE: This code is working perfectly. but someone saying this is bad practice **

module.service('storageService', [function () {
    this.getValue=function(){//} 
    this.computeExpiry=function(){
       var activeRule=this.getValue() //using `this` to call getValue function is bad practice  ?? 
     }  

  }]);

It would be appreciable somebody can give some insight.

1.) Is the above code wrong/bad practice?.

2.) Should I always proxy that=this in angular js services to call the function inside the same service

3.) The above code lenient?

4.) "The above code causes unexpected bug because the services are injected in different execution contexts so the this will point to different context " how valid this statement how this affect.