Dependency injection in Angular 2 pipes

Greetings everyone! I'm a newcomer to angular 2 and currently trying my hand at creating a custom pipe/filter. However, I've encountered an issue when attempting to inject the pipe I created inside app.ts as shown in the image linked here.

Here is my component code:

import { Component, OnInit ,Pipe, PipeTransform} from '@angular/core';
import { Input, Injectable, ApplicationRef, ChangeDetectorRef } from '@angular/core';
import {Observable} from 'rxjs/Rx'
import {Filter} from '../filter.pipe';

@Component({
  selector: 'app-test',
  templateUrl: './test.component.html',
  styleUrls: ['./test.component.css'],
  pipesp[Filter]
  
})

export class TestComponent implements PipeTransform  {
    private todos = ['wash dishes', 'Clean the ground','program the site', 'eat'];
  constructor() {
  }

   transform(value: any) {
    if (!value) {
      return '';
    }
    
  }
}

And here's the code for filter.pipe.ts:

import  {Pipe, PipeTransform} from  '@angular/core';
@Pipe({name:'filter'})
export class Filter {
    transform(value,args){
        if(!args[0]){
            return value;
        }else if ( value){
            return value.filter(item => {
                for(let key in item){
                    if((typeof item[key] === 'string' || item[key] instanceof String) && (item[key].indexOf(args[0]) !==-1)){
                        return true;
                    }
                }
            });
        }
    }

}

Lastly, let's take a look at test.component.html:

<input type="text" [(ngModel)]="filterText">
<ul>
    <li *ngFor="let todo of todos | filter: filterText "> 
        {{todo}}
    </li>
</ul>

Answer №1

Make sure to include the Pipe in the appropriate module and reference it in the component like this:

 declarations: [
    Filter
]

Answer №2

To ensure the Pipe Component is available globally in all components within your Angular application, you must include it in the Ng Module defined within the root component module.

@NgModule({
  imports:      [ BrowserModule ],
  declarations: [ CustomPipe ],
  bootstrap:    [ AppComponent ]
})

You can then directly utilize the Pipe Component in your templates:

@Component({
  selector: 'my-app',
  template: '<p>Hello, my name is <strong>{{ name | custom}}</strong>.</p>', 
})

Answer №3

Check out this solution

Include the following code snippet in your component:

@Component({
  pipes: [ filter ] 
})

Do not use this alternative syntax:

@Component({
  pipes[Filter]
})

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