What is wrong with my Angular code? I am getting the following error: Cannot read property 'remove' of undefined at BrowserDomAdapter.removeClass <ol> <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> Continue reading...