Answer by Aishwarya Kathavarayan for Angular: conditional class with *ngClass

Try Like this..

Define your class with ''

<ol class="breadcrumb"><li *ngClass="{'active': step==='step1'}" (click)="step='step1; '">Step1</li><li *ngClass="{'active': step==='step2'}"  (click)="step='step2'">Step2</li><li *ngClass="{'active': step==='step3'}" (click)="step='step3'">Step3</li></ol>