Angular：带* ngClass的条件类

我的Angular代码有什么问题？我正进入（状态：

Cannot read property 'remove' of undefined at BrowserDomAdapter.removeClass ...

的HTML

<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>