Angular io (4) *ngFor first and last

Question

I am trying to tell whether an item in an *ngFor is the first or last element to style a container. Is there a way to do something like this?

<md-expansion-panel *ngFor="let item of items" *ngClass="{ 'first' : item.isFirst }">
  <content></content>
</md-expansion-panel>

Thanks for any help offered!

Answer 1

Inside the ngFor you have access to several variables:

• index: number: The index of the current item in the iterable.
• first: boolean: True when the item is the first item in the iterable.
• last: boolean: True when the item is the last item in the iterable.
• even: boolean: True when the item has an even index in the iterable.
• odd: boolean: True when the item has an odd index in the iterable.

So:

<md-expansion-panel *ngFor="let item of items; first as isFirst"
    *ngClass="{ 'first' : isFirst }">
  <content></content>
</md-expansion-panel>

Documentation at https://angular.io/api/common/NgForOf gives this example:

<li *ngFor="let user of userObservable | async as users; index as i; first as isFirst">
   {{i}}/{{users.length}}. {{user}} <span *ngIf="isFirst">default</span>
</li>

Answer 2

This how you can do it :

<md-expansion-panel *ngFor="let item of items; let first = first; 
      let last = last" *ngClass="{ 'first' : first }">
   <content></content>
 </md-expansion-panel>

NgFor provides several exported values that can be aliased to local variables:

• index will be set to the current loop iteration for each template context so it start from 0.

• first will be set to a boolean value indicating whether the item is the first one in the iteration.

• last will be set to a boolean value indicating whether the item is the last one in the iteration.

• even will be set to a boolean value indicating whether this item has an even index.

• odd will be set to a boolean value indicating whether this item has an odd index.

for more information : NgFor-directive 🚀🚀