NgAs

Angular pipe and directive for type casting template variables.

Description

Sometime there is a need to cast variable into component template as some type. This library has pipe and directive for type casting template variables and improve IDE suggestion and refactoring.

See the stackblitz demo.

Get Started

Step 1: install ng-as

npm i ng-as

Step 2: Import NgAsModule into your app module, eg.:

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { AppComponent } from './app.component';

import { NgAsModule } from 'ng-as';

@NgModule({
  declarations: [AppComponent],
  imports: [
    BrowserModule,
    CommonModule,
    NgAsModule,
  ],
  providers: [],
  bootstrap: [AppComponent],
  ],
})
export class AppModule { }

Step 3: usage

type casting template variables with directirve eg.:

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

// your interface, but also work with any typescript type (class, type, etc.)
interface Person {
  name: string;
}

@Component({
  selector: 'app-root',
  template: `
  <ng-container *ngTemplateOutlet="personTemplate; context: {$implicit: person}"></ng-container>

  <ng-template #personTemplate [ngAs]="Person" let-person>
    <span>Hello {{ person.name }}!</span>
  </ng-template>
  `,
})
export class AppComponent {
  // NOTE: If you have "strictPropertyInitialization" enabled, 
  // you will need to add a non-null assertion (!)
  public Person!: Person; // publish your interface into html template
  person: Person = { name: 'Simone' }; // the data
}

type casting template variables with pipe eg.:

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

// your interface, but also work with any typescript type (class, type, etc.)
interface Person {
  name: string;
}

@Component({
  selector: 'app-root',
  template: `
  <ng-container *ngTemplateOutlet="personTemplate; context: {$implicit: person}"></ng-container>

  <ng-template #personTemplate let-person>
    <span>Hello {{ (person | as: Person).name }}!</span>
  </ng-template>
  `,
})
export class AppComponent {
  // NOTE: If you have "strictPropertyInitialization" enabled, 
  // you will need to add a non-null assertion (!)
  public Person!: Person; // publish your interface into html template
  person: Person = { name: 'Simone' }; // the data
}

That's all!

Example: MatTable

matCellDef cannot infer the type of its parent's input. But with ng-as you can strong-type its template variable.

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

export interface PeriodicElement {
  name: string;
  position: number;
  weight: number;
  symbol: string;
}

const ELEMENT_DATA: PeriodicElement[] = [
  {position: 1, name: 'Hydrogen', weight: 1.0079, symbol: 'H'},
  {position: 2, name: 'Helium', weight: 4.0026, symbol: 'He'},
  {position: 3, name: 'Lithium', weight: 6.941, symbol: 'Li'},
  {position: 4, name: 'Beryllium', weight: 9.0122, symbol: 'Be'},
  {position: 5, name: 'Boron', weight: 10.811, symbol: 'B'},
  {position: 6, name: 'Carbon', weight: 12.0107, symbol: 'C'},
  {position: 7, name: 'Nitrogen', weight: 14.0067, symbol: 'N'},
  {position: 8, name: 'Oxygen', weight: 15.9994, symbol: 'O'},
  {position: 9, name: 'Fluorine', weight: 18.9984, symbol: 'F'},
  {position: 10, name: 'Neon', weight: 20.1797, symbol: 'Ne'},
];

@Component({
  selector: 'table-basic-example',
  template: `
  <table mat-table [dataSource]="dataSource" class="mat-elevation-z8">

    <ng-container matColumnDef="position">
      <th mat-header-cell *matHeaderCellDef> No. </th>
      <td mat-cell *matCellDef="let element"> {{(element | as: PeriodicElement).position}} </td>
    </ng-container>

    <ng-container matColumnDef="name">
      <th mat-header-cell *matHeaderCellDef> Name </th>
      <td mat-cell *matCellDef="let element"> {{(element | as: PeriodicElement).name}} </td>
    </ng-container>

    <ng-container matColumnDef="weight">
      <th mat-header-cell *matHeaderCellDef> Weight </th>
      <td mat-cell *matCellDef="let element"> {{(element | as: PeriodicElement).weight}} </td>
    </ng-container>

    <ng-container matColumnDef="symbol">
      <th mat-header-cell *matHeaderCellDef> Symbol </th>
      <td mat-cell *matCellDef="let element"> {{(element | as: PeriodicElement).symbol}} </td>
    </ng-container>

    <tr mat-header-row *matHeaderRowDef="displayedColumns"></tr>
    <tr mat-row *matRowDef="let row; columns: displayedColumns;"></tr>
  </table>
  `,
})
export class TableBasicExample {
  PeriodicElement!: PeriodicElement;
  displayedColumns: string[] = ['position', 'name', 'weight', 'symbol'];
  dataSource = ELEMENT_DATA;
}

Support

This is an open-source project. Star this repository, if you like it, or even donate. Thank you so much!

My other libraries

I have published some other Angular libraries, take a look:

• NgSimpleState: Simple state management in Angular with only Services and RxJS
• NgHttpCaching: Cache for HTTP requests in Angular application
• NgGenericPipe: Generic pipe for Angular application for use a component method into component template.
• NgLet: Structural directive for sharing data as local variable into html component template
• NgForTrackByProperty: Angular global trackBy property directive with strict type checking