Angular 16 NgFor Directive Tutorial with Examples

Last Updated on by in Angular
In this Angular NgFor Directive tutorial, we are going to understand how to use NgFor directive in angular application.NgFor is a structural directive in Angular that is used to iterate over a collection of items and generate HTML elements for each item.

It is typically used with an array or an iterable object in Angular templates to generate a dynamic list of items.

The NgFor is a built-in structural directive, and it is used to loop over a data list and arrays to show the result on front-end.

The *ngFor directive is implemented with HTML template this directive goes through every item in the data collection.

NgFor shows the result when we pass the NgFor’s value in the double-curly braces.

No Property Access From Index Signature

To resolve error:

Property ‘xxxName’ comes from an index signature, so it must be accessed with [‘xxxName’]

This setting makes sure profound consistency between accessing a field via the “dot” (obj.key) syntax, and “indexed” (obj["key"]) and the way which the property is declared in the type.

Without this flag, TypeScript will allow you to use the dot syntax to access fields which are not defined:

Make sure to set noPropertyAccessFromIndexSignature property to false under compilerOptions in tsconfig.json file:

"compilerOptions": {
 ...
 ...
   "strict": false,
   "noPropertyAccessFromIndexSignature": false,
 ...
 ...
}

Angular NgFor Examples

In order to remove strict type warnings or errors make sure to set “strict”: false and "strictTemplates": false under compilerOptions and angularCompilerOptions properties in tsconfig.json file.

In the following example we curated a movies list, you’ll see how we are using *ngFor directive to display the movies name using Angular *ngFor directive.

import { Component } from '@angular/core';

@Component({
  selector: 'my-app',
  template: `
    <ul>
      <li *ngFor="let movie of Movies">
        {{ movie.name }}
      </li>
    </ul>
    `
})

export class AppComponent  {
    Movies: any[] = [
    {
      "name": "Avengers: Endgame"
    },
    {
      "name": "Good Boys"
    },
    {
      "name": "Playmobil: The Movie"
    },
    {
      "name": "Aquarela"
    },
    {
      "name": "Aladdin"
    }, 
    {
      "name": "Downton Abbey"
    }
  ];
}

You will see below output for the above programme:

# Avengers: Endgame
# Good Boys
# Playmobil: The Movie
# Aquarela
# Aladdin
# Downton Abbey

Get Current Items Index using Angular NgFor Directive

In the next step, we will learn to get the current item’s index using *ngFor tag. This can be done very easily using the index variable with ngFor. Have a look in the given below example.

import { Component } from '@angular/core';

@Component({
  selector: 'my-app',
  template: `
    <ul>
      <li *ngFor="let movie of Movies; let i = index">
        {{ i + 1 }} : {{ movie.name }}
      </li>
    </ul>
   `
})

export class AppComponent  {
    Movies: any[] = [
    {
      "name": "Avengers: Endgame"
    },
    {
      "name": "Good Boys"
    },
    {
      "name": "Playmobil: The Movie"
    },
    {
      "name": "Aquarela"
    },
    {
      "name": "Aladdin"
    }, 
    {
      "name": "Downton Abbey"
    }
  ];
}

Have a look at items index in the following example:

1 : Avengers: Endgame
2 : Good Boys
3 : Playmobil: The Movie
4 : Aquarela
5 : Aladdin
6 : Downton Abbey

As you can see we declared the let i = index with *ngFor directive, we are using the i within the double curly braces. One important thing to remember is the index always starts from 0.

Set First and Last Item Class Name

In this example we’ll learn how to target first and last item in a list and set the class name using Angular *ngFor directive.

import { Component } from '@angular/core';

@Component({
  selector: 'my-app',
  template: `
    <ul>
      <li 
         *ngFor="let movie of Movies; let first = first; 
         let last = last" [ngClass]="{ first: first, last: last }">
           {{ movie.name }}
      </li>
    </ul>
   `
})


export class AppComponent  {
    Movies: any[] = [
    {
      "name": "Avengers: Endgame"
    },
    {
      "name": "Good Boys"
    },
    {
      "name": "Playmobil: The Movie"
    },
    {
      "name": "Aquarela"
    },
    {
      "name": "Aladdin"
    }, 
    {
      "name": "Downton Abbey"
    }
  ];
}

Above programme will add the CSS class by the name of first and last in HTML list’s 1st and last element.

Nested NgFor

In the next example, we’ll learn how to loop over nested data list using ngFor structured directive.

import { Component } from '@angular/core';

@Component({
  selector: 'my-app',
  template: `
    <ul *ngFor="let collection of industryType">
      <li>{{ collection.type }}</li>
      <ul>
        <li *ngFor="let hollywood of collection.movies">
          {{ hollywood.name }}
        </li>
      </ul>
    </ul>
    `
})

export class AppComponent {
  industryType: any[] = [
    {
      'type': 'Bollywood',
      'movies': [
        {
          "name": "Gully Boy"
        },
        {
          "name": "Manikarnika"
        },
        {
          "name": "Kalank"
        }        
      ]
    },
    {
      'type': 'Hollywood',
      'movies': [
        {
          "name": "Avengers: Endgame"
        },
        {
          "name": "Good Boys"
        },
        {
          "name": "Playmobil"
        },
        {
          "name": "Aquarela"
        }        
      ]
    }
  ];
}

As you can see we have an industryType array which contains Bollywood and Hollywood movies. We used the ngFor directive to loop over the movies group and showed the results.

NgFor Track By

The trackBy method helps in keeping track of collection elements in Angular.

By default, Angular doesn’t track if any item is being added or removed in the collection. Angular offers trackBy feature it can be used with *ngFor directive.

The trackBy feature enhances performance by putting less weight in DOM.

In order to use trackBy with NgFor, we should declare a function inside the component class and map it to the ngFor directive as given below:

import { Component } from '@angular/core';

@Component({
  selector: 'my-app',
  template: `
    <ul>
      <li *ngFor="let movie of Movies; trackBy: trackByFn">
        {{ movie.name }}
      </li>
    </ul>
    `
})

export class AppComponent {

    Movies: any[] = [
    {
      "id": 1,
      "name": "Avengers: Endgame"
    },
    {
      "id": 2,
      "name": "Good Boys"
    },
    {
      "id": 3,
      "name": "Playmobil: The Movie"
    },
    {
      "id": 4,
      "name": "Aquarela"
    },
    {
      "id": 5,
      "name": "Aladdin"
    }, 
    {
      "id": 6,
      "name": "Downton Abbey"
    }
  ];

  // TrackBy
  trackByFn(index:number, movie:any): number {
    return movie.id;
  }
}

Conclusion

Finally, we are done with Angular NgFor Directive tutorial with examples. In this tutorial, we have seen how to iterate over a data collection using ngFor directive.

We used ngFor to get the current item Index, set the first and last element CSS class name, loop over nested data collection and learnt to use the trackBy method.

Digamber - Author positronX.io

Hi, I'm Digamber Singh, a New Delhi-based full-stack developer, tech author, and open-source contributor with 10+ years' experience in HTML, CSS, JavaScript, PHP, and WordPress.