index for in angular

<ul>
    <li *ngFor="let item of items; let i = index" [attr.data-index]="i">
        {{item}}
    </li>
</ul>

You have to use let to declare the value rather than #.

<ul>
    <li *ngFor="let item of items; let i = index" [attr.data-index]="i">
        {{item}}
    </li>
</ul>
Angular = 1
<ul>
    <li *ngFor="#item of items; #i = index" [attr.data-index]="i">
        {{item}}
    </li>
</ul>