Angular 2 ngfor first, last, index loop

Question

I'm trying to set as default the first occurrence in this example: plunkr

getting the following error:

    Unhandled Promise rejection: Template parse errors:
    TypeError: Cannot read property 'toUpperCase' of undefined ("dButtonToggleGroup">
    <md-button-toggle [ERROR ->]*ngFor="let indicador of indicadores; #first = first" value="indicador.id" [checked]="first">"): ng:///AppModule/HomeComponent.html@35:78
    Parser Error: Unexpected token #, expected identifier, keyword, or string at column 31 in [let indicador of indicadores; #first = first] in ng:///AppModule/HomeComponent.html@35:78 ("<md-button-toggle *ngFor="let indicador of indicadores; #first = first" value="indicador.id" [ERROR ->][checked]="first">
    <span>{{ indicado"): ng:///AppModule/HomeComponent.html@35:153

what is wrong??

Answer 1

Check out this plunkr.

When you're binding to variables, you need to use the brackets. Also, you use the hashtag when you want to get references to elements in your html, not for declaring variables inside of templates like that.

<md-button-toggle *ngFor="let indicador of indicadores; let first = first;" [value]="indicador.id" [checked]="first"> 

---

Edit: Thanks to Christopher Moore: Angular exposes the following local variables:

• index
• first
• last
• even
• odd

Answer 2

Here is how its done in Angular 6

    <li *ngFor="let user of userObservable ; first as isFirst">
       <span *ngIf="isFirst">default</span>
    </li>

Note the change from let first = first to first as isFirst

Answer 3

By this you can get any index in *ngFor loop in ANGULAR ...

<ul>
  <li *ngFor="let object of myArray; let i = index; let first = first ;let last = last;">
    <div *ngIf="first">
       // write your code...
    </div>

    <div *ngIf="last">
       // write your code...
    </div>
  </li>
</ul>

We can use these alias in *ngFor

• index : number : let i = index to get all index of object.
• first : boolean : let first = first to get first index of object.
• last : boolean : let last = last to get last index of object.
• odd : boolean : let odd = odd to get odd index of object.
• even : boolean : let even = even to get even index of object.