Angular 2 ngFor - reverse order of output using th

Question

Trying to learn something about filtering and ordering in Angular 2. I can't seem to find any decent resources and I'm stuck at how to order an ngFor output in reverse order using the index. I have written the the following pipe put it keeps giving me errors that array slice in not a function.

@Pipe({
    name: 'reverse'
})
export class ReversePipe implements PipeTransform {
    transform(arr) {
        var copy = arr.slice();
        return copy.reverse();
    }
}

and my ngfor looks like this.

<div class="table-row generic" *ngFor="let advert of activeAdverts | reverse let i = index;" [attr.data-index]="i" (click)="viewAd(advert.title)">      
    <div class="table-cell white-text">{{ i+1 }}</div>                    
    <div class="table-cell white-text">{{advert.title}}</div>
    <div class="table-cell green-text">{{advert.advert}}</div>
</div>

Answer 1

Using the following method u can reverse the output, but orignal array won't be modified,

 <tr *ngFor="let advert of activeAdverts; let i = index" >
           <td>{{activeAdverts[activeAdverts.length-i-1]}}</td>
  </tr>

Answer 2

The most simple way I was able to make it work is to just use activeAdverts.reverse(). In your case:

<div class="table-row generic" *ngFor="let advert of activeAdverts.reverse() let i = index;" [attr.data-index]="i" (click)="viewAd(advert.title)">      
    <div class="table-cell white-text">{{ i+1 }}</div>                    
    <div class="table-cell white-text">{{advert.title}}</div>
    <div class="table-cell green-text">{{advert.advert}}</div>
</div>

I found this answer to do the trick

Answer 3

For such common use cases, I would suggest you to use reverse pipe from ng-pipes module: https://github.com/danrevah/ng-pipes#reverse-1

From the DOCS:

in the controller:

this.items = [1, 2, 3];

in the view:

<li *ngFor="let item of items | reverse"> <!-- Array: [3, 2, 1] -->

Answer 4

I think @BhaskerYadav gave the best answer. Changing the original array is a bad idea and his/her idea has no side-effects, performance or otherwise. IMHO it just needs a slight improvement as all that index dereferencing is unreadable at scale.

<tr *ngFor="let _ of activeAdverts; let i = index">
  <ng-container *ngIf="activeAdverts[activeAdverts.length-i-1] as advert">
    <td>{{advert.p}}</td>
    <td>{{advert.q}}</td>
    ...
  </ng-container>
</tr>

Answer 5

I would add .slice() as well

*ngFor="let advert of activeAdverts.slice().reverse() let i = index;"