Angular 2 Form builder validators question

[LearningAngular]

Hello,

Looking at the code below. 

I'm trying to enter a default value with this line of code controlerSeverity:[2,[]], but i like to make this value more dynamic so rather then hard code the value in this example the number two can I not substitute a variable (second example code)

This works:

 buildDetailsForm() {

    this.DetailsForm = this._fb.group({          

     incidentDescription: ['', []],

     controlerSeverity:[2,[]], // hard coded value works

     createdBy:['',[]]

   });

    }

This does not work, how come?

testValue = 2;

 buildDetailsForm() {

    this.DetailsForm = this._fb.group({          

     incidentDescription: ['', []],

     controlerSeverity:[this.testValue,[]], // can i not use a variable in place of hard coding for example a number??? as of now this wont work.

     createdBy:['',[]]

   });

    }