[ngClass]="{'my-class': step=='step1'}"
[ngClass]="(step=='step1')?'my-class1':'my-class2'"
[class.my-class]="step=='step1'"
[ngClass]="{'my-class': step=='step1', 'my-class2':step=='step2' }"
[ngClass]="{1:'my-class1',2:'my-class2',3:'my-class4'}[step]"
