Creating Class Names Dynamically in Angular 2 Using ngFor Index

Question

Creating Class Names Dynamically in Angular 2 Using ngFor Index

Encountering an issue while trying to generate a dynamic class name based on the ngFor loop index in Angular 2. Due to restrictions, I had to use a specific syntax as Angular 2 does not support ngFor and ngIf together on the same element.

Given this setup, how can I dynamically set a class name using the value of index at {{index}}? Although this may not adhere strictly to A2 standards, I included it in the example code to indicate where I aim to insert the value.

<div class="product-detail__variants">
    <template ngFor #variant [ngForOf]="variants" #index="index">
        <div *ngIf="currentVariant == index">
            <div class="product-detail-carousel-{{index}}">

            </div>
        </div>
    </template>
</div>

The variable "variants" stands for an empty array with a specific length, hence "variant" holds no actual value.

"currentVariant" denotes a number that typically begins at 0.

UPDATE: The provided code is accurate. My previous issue stemmed from an unrelated error that I mistakenly associated with this piece of code.

javascript typescript angular

Answer 1

Answer №1

I must admit, your problem is a bit puzzling ;-)

When it comes to assigning classes to specific elements, there are two main approaches:

The first method involves using curly brackets like so:

@Component({
  selector: 'my-app',
  template: `
    <div class="product-detail__variants">
      <template ngFor #variant [ngForOf]="variants" #index="index">
        <div *ngIf="currentVariant == index">
          <div class="product-detail-carousel-{{index}}">
            Test
          </div>
        </div>
      </template>
    </div>
  `,
  styles: [
    '.product-detail-carousel-2 { color: red }'
  ]
})

In this scenario, the text "Test" will only appear for the third item (with an index of 2) and will be styled in red.

Alternatively, you can utilize the ngClass directive as recommended by @Langley:

import {NgClass} from 'angular2/common';

@Component({
  selector: 'my-app',
  template: `
    <div class="product-detail__variants">
      <template ngFor #variant [ngForOf]="variants" #index="index">
        <div *ngIf="currentVariant == index">
          <div class="product-detail-carousel-{{index}}">
            Test
          </div>
        </div>
      </template>
    </div>
  `,
  styles: [
    '.product-detail-carousel-2 { color: red }'
  ],
  directives: [ NgClass ]
})

The key difference here is that you'll need to include the NgClass directive within the providers section of your component definition. Once again, "Test" will only be visible for the third element (index 2) and will be displayed in red.

Your statement regarding "The variants array being empty with set length and the variant having no value, while currentVariant defaulting to 0" raises the question of what you expect to see when iterating over an empty array using ngFor...

Hoping this sheds some light on the matter, Thierry

Answer 2

I must admit, your problem is a bit puzzling ;-)

When it comes to assigning classes to specific elements, there are two main approaches:

The first method involves using curly brackets like so:

@Component({
  selector: 'my-app',
  template: `
    <div class="product-detail__variants">
      <template ngFor #variant [ngForOf]="variants" #index="index">
        <div *ngIf="currentVariant == index">
          <div class="product-detail-carousel-{{index}}">
            Test
          </div>
        </div>
      </template>
    </div>
  `,
  styles: [
    '.product-detail-carousel-2 { color: red }'
  ]
})

In this scenario, the text "Test" will only appear for the third item (with an index of 2) and will be styled in red.

Alternatively, you can utilize the ngClass directive as recommended by @Langley:

import {NgClass} from 'angular2/common';

@Component({
  selector: 'my-app',
  template: `
    <div class="product-detail__variants">
      <template ngFor #variant [ngForOf]="variants" #index="index">
        <div *ngIf="currentVariant == index">
          <div class="product-detail-carousel-{{index}}">
            Test
          </div>
        </div>
      </template>
    </div>
  `,
  styles: [
    '.product-detail-carousel-2 { color: red }'
  ],
  directives: [ NgClass ]
})

The key difference here is that you'll need to include the NgClass directive within the providers section of your component definition. Once again, "Test" will only be visible for the third element (index 2) and will be displayed in red.

Your statement regarding "The variants array being empty with set length and the variant having no value, while currentVariant defaulting to 0" raises the question of what you expect to see when iterating over an empty array using ngFor...

Hoping this sheds some light on the matter, Thierry

Answer 3

Answer №2

If you are interested in dynamically adding a specific class based on the index, here's a neat way to achieve that. I find this syntax quite intuitive as well. For example, if you want to assign the class last-para to the last paragraph in an array:

<p
  *ngFor="let p of paragraphs; let i = index"
  [class.last-para]="i >= paragraphs.length - 1">
  {{p}}</p>

Answer 4

If you are interested in dynamically adding a specific class based on the index, here's a neat way to achieve that. I find this syntax quite intuitive as well. For example, if you want to assign the class last-para to the last paragraph in an array:

<p
  *ngFor="let p of paragraphs; let i = index"
  [class.last-para]="i >= paragraphs.length - 1">
  {{p}}</p>

Creating Class Names Dynamically in Angular 2 Using ngFor Index

Answer №1

Answer №2

Similar questions

Focusing on the active element in Typescript

How to Monitor Store Changes within a Vue File Using Vue.js

Absence of skins and themes in TinyMCE (Angular)

Choice of product variations as a package

Invoking a function within an HTML file does not result in triggering an alert message

Ways to resolve issues related to null type checking in TypeScript

Spin the Three.js camera in a circular motion along the Y-axis

Sending data using Ajax to the server-side code in ASP.NET

Utilize a variable within an HTML attribute

perform an action if any division element is void of content

Using AJAX to update content based on selected value in a dropdown menu

Prevent legend strike-through on click in Vue Chart.js

When using jQuery with a large selectbox, you may encounter the error message: "Uncaught RangeError: Maximum

Failure to Present Outcome on Screen

Utilizing AJAX within a Rails application to dynamically alter a database field without the need for a traditional form

Extending an interface in TypeScript does not permit the overriding of properties

I'm having trouble importing sqlite3 and knex-js into my Electron React application

Why is the mappable Observable lost after using Angular 5's HttpClient?

Difficulty with Nuxt + Vuex: Retrieving data from state using getter

What is the best way to reduce the file size of a group of PNG images for