Track by pipe for Angular

track-by-key.pipe.ts

import {NgModule, Pipe, PipeTransform} from '@angular/core';

@Pipe({
  name: 'trackByKey',
  pure: true,
})
export class TrackByKeyPipe implements PipeTransform {
  public transform(key: string) {
    return (index, value) => {
      return value[key];
    };
  }
}

@NgModule({
  declarations: [TrackByKeyPipe],
  exports: [TrackByKeyPipe],
})
export class TrackByKeyPipeModule {}

Usage:

<ng-container *ngFor="let user of users; trackBy: 'id' | trackByKey">
  <!-- code -->
</ng-container>