Angular2 - How to Condition Import, Does More Import Slow Down the Performance?

I have this:

import {StepOnePage} from '../../pages/step-one/step-one';
import {StepTwoPage} from '../../pages/step-two/step-two';
import {StepThreePage} from '../../pages/step-two/step-one';
import {StepFourPage} from '../../pages/step-two/step-one';
import {StepFivePage} from '../../pages/step-two/step-one';

How can I put condition in these import statements?

I tried to import in the constructor, so I can apply the condition:

If currentStep is 'Step1' 
    then import StepTwoPage

however, it gives me this error:

EXCEPTION: Error: Uncaught (in promise): Unexpected directive value 'undefined' on the View of component 'StepOnePage'

Or I can import everything as another solution, however, I'm worried about the performance issue that there are more than necessary imports in a page.

Please advice. Thanks.