I am trying to declare an index in *ngFor but I am getting a type error and it is saying

<div class='text' *ngFor='let item of blogs; let i = index | async | filter : 'feat' : true'>

If I take out let i = index it works fine, but I want to use the index, so I can apply css classes to the elements. Looking at documentation, this is how you are supposed to do it.