Skip to main content

Angular 2 Pipes in Depth [Custom Pipes and Inbuilt Pipes with Examples]

This post helps us to learn “Angular 2 Pipes in Depth” and we will cover most of all questions and answers related to the pipes.

1.      What is Pipes?
2.      Why use Pipes?
4.      What is Async Pipe?

What is Pipes?
“Pipes transform displayed values within a template.”

Sometimes, the data is not displays in the well format on the template that time where using pipes.
You also can execute a function in the template to get its returned value.

The angular 2 have some additional pipes names that are async, decimal, percept and so on. And also some of pipes not supported in angular 2 that are number, orderBy and filter and these are archiving using “custom pipes”.

Key Points:-
Pipe class implements the “PipeTransform” interfaces transform method that accepts an input value and returns the transformed result.

There will be one additional argument to the transform method for each parameter passed to the pipe.

The “@Pipe” decorator allows us to define the pipe name that is globally available for use in any template in the across application.

For example as,
import { Pipe, PipeTransform } from '@angular/core';

@Pipe({
    name: 'barcode',
    pure: false
})
export class BarCodePipe implements PipeTransform {
    transform(value: string, args: any[]): string {
        if (!value) {
            return '';
        }
        return "****-****_" + (value.length > 8 ? (value.length - 8): '')
    }
}

Angular 2 Built-in Pipes:-
1.      DatePipe,
2.      UpperCasePipe,
3.      LowerCasePipe,
4.      CurrencyPipe,
5.      PercentPipe,
6.      JsonPipe,
7.      AsyncPipe,
8.      And so on..

The following table shows a comparison between Angular 1.x and Angular 2.

 Why use Pipes?
Sometimes, the data is not displays in the correct format on the template that time where using pipes.

You also can execute a function in the template to get its returned value.

For example as,

If you want to display the bank card number on your account detail templates that how to displays this card number?  I think you should display the last four digits and rest of all digits will display as encrypted like (****-****-****_and your card numbers) that time you will need to create a custom pipe to achieve this.

What is a pure and impure pipe?
In Angular 2, there are two types of pipes i.e.
1.      pure
2.      impure

The pure pipe is by default. Every pipe has been pure by default. If you want to make a pipe impure that time you will allow the setting pure flag to false.

Pure Pipes:-

Angular executes a pure pipe only when it detects a pure change to the input value. A pure change can be primitive or non-primitive.

Primitive data are only single values, they have not special capabilities and the non-primitive data types are used to store the group of values.

For example for pipe pure,
import { Pipe, PipeTransform } from '@angular/core';

@Pipe({
    name: 'barcode'
})
export class BarCodePipe implements PipeTransform {
    transform(value: string, args: any[]): string {
        if (!value) {
            return '';
        }
        return "****-****_" + (value.length > 8 ? (value.length - 8): '')
    }
}

Impure Pipes:-

Angular executes an impure pipe during every component change detection cycle. An impure pipe is called often, as often as every keystroke or mouse-move. If you want to make a pipe impure that time you will allow the setting pure flag to false.

For example for pipe impure,
import { Pipe, PipeTransform } from '@angular/core';

@Pipe({
    name: 'barcode',
    pure: false
})
export class BarCodePipe implements PipeTransform {
    transform(value: string, args: any[]): string {
        if (!value) {
            return '';
        }
        return "****-****_" + (value.length > 8 ? (value.length - 8): '')
    }
}


What is Async Pipe?

Angular 2 provides us special kinds of pipe that is called Async pipe and the Async pipe subscribes to an Observable or Promise and returns the latest value it has emitted.

The Async pipe allows us to bind our templates directly to values that arrive asynchronously manner and this is the great ability for the promises and observables.

Example for AsyncPipe with Promise using NgFor,

@Component({
    selector: 'app-promise',
    template: '<ul> < li * ngFor="let user of users | async">  Id: {{user.id }}, Name: {{user.name }} </li>< /ul>'
})
export class PromiseComponent {
    //USERS DECLARATIONS.
    users = [];

    //FETCHING JSON DATA FROM REST APIS
    userRestApiUrl: string = 'https://api.github.com/users/hadley/orgs';

    //HOME COMPONENT CONSTRUCTOR
    constructor(private userService: UserService) { }

    //GET USERS SERVICE ON PAGE LOAD.
    ngOnInit() {
        this.userService.getUsers(this.userRestApiUrl).subscribe(data => this.users = data);
    }
}

How to create a custom Pipes?
How to create a globally available custom “Pipe”?

The “@Pipe” decorator allows us to define the pipe name that is globally available for use in any template in the across application.

Steps for Creating a Custom Pipe:-
1.      Create a typescript class.
2.      Decorate the class using @Pipe.
3.      Implement PipeTransform interface.
4.      Override transform() method.
5.      Configure the class in application module with @NgModule.
6.      Ready to use our custom pipe anywhere in application.

In the below example,

I am using the custom pipe in the user temple to display our custom “Ids” values at the place of Id.

Table of Component
1.      user.component.ts
2.      user.service.ts
3.      custom.barcode.pipe.ts
4.      app.module.ts
5.      user.component.html

user.component.ts :-
import { Component, Injectable} from '@angular/core';
import { CommonModule } from '@angular/common';
import { HttpModule, Http } from '@angular/http';
import { UserService } from '../shared/service/user.service';
import { BarCodePipe } from '../shared/pipe/custom.barcode.pipe';

@Component({
    selector: 'user',
    templateUrl: './user.component.html',
    styleUrls: ['./user.component.css']
})

export class UserComponent {
    //USERS DECLARATIONS.
    users = [];

    //FETCHING JSON DATA FROM REST APIS
    userRestApiUrl: string = 'https://api.github.com/users/hadley/orgs';

    //HOME COMPONENT CONSTRUCTOR
    constructor(private userService: UserService) {  }

    //GET USERS SERVICE ON PAGE LOAD.
    ngOnInit() {
        this.userService.getUsers(this.userRestApiUrl).subscribe(data => this.users = data);
    }
}
//END BEGIN - USERCOMPONENT

user.service.ts :-

import { Injectable } from '@angular/core';
import { Http, Response } from '@angular/http';
import 'rxjs/add/operator/map';

//BEGIN-REGION - USERSERVICE
@Injectable()
export class UserService {
    constructor(private _http: Http) {
    }

    getUsers(apiUrl) {
        return this._http.get(apiUrl).map((data: Response) => data.json());
    }
}
//END BEGIN – USERSERVICE

custom.barcode.pipe.ts :-

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

@Pipe({
    name: 'barcode',
    pure: false
})
export class BarCodePipe implements PipeTransform {
    transform(value: string, args: any[]): string {
        if (!value) {
            return '';
        }
        return "....-" + (value.length > 2 ? (value.length - 2) : '')
    }
}

app.module.ts :-

import { NgModule } from '@angular/core';
import { RouterModule, Routes } from '@angular/router';
import { UniversalModule } from 'angular2-universal';
import { FormsModule, ReactiveFormsModule } from '@angular/forms';
import { HttpModule } from '@angular/http';
import { AppComponent } from './components/app/app.component';
import { UserComponent } from './components/user/user.component';
import { HeaderComponent } from './components/shared/header/header.component';
import { MenuComponent } from './components/menu/menu.component';
import { LoginComponent } from './components/login/login.component';
import { RegistrationComponent } from './components/registration/registration.component';
import { UserService } from './components/shared/service/user.service';
import { BarCodePipe } from './components/shared/pipe/custom.barcode.pipe';
import { MyPipePipe } from './components/shared/pipe/test.pipes';

@NgModule({
    bootstrap: [ AppComponent ],
    declarations: [
        AppComponent,
        UserComponent,
        HeaderComponent,
        MenuComponent,
        LoginComponent,
        RegistrationComponent,
        BarCodePipe,
        MyPipePipe
    ],
    imports: [
        UniversalModule, // MUST BE FIRST IMPORT. THIS AUTOMATICALLY IMPORTS BROWSERMODULE, HTTPMODULE, AND JSONPMODULE TOO.
        RouterModule.forRoot([ //RouterModule.forRoot method in the module imports to configure the router.
            { path: '', redirectTo: 'user', pathMatch: 'full' },
            { path: 'user/:id', component: UserComponent }, //HERE ID IS A ROUTE PARAMETER.
            { path: 'login', component: LoginComponent },
            { path: 'registration', component: RegistrationComponent },
            { path: '**', redirectTo: 'user' }
        ]),
        FormsModule,
        ReactiveFormsModule       
    ],
    providers: [UserService]
})
export class AppModule {
}

user.component.html :-

<div class="row">
<div class="col-lg-12">
    <div class="ibox float-e-margins">
        <div class="ibox-title">
            <h2>Angular 2 - User Services</h2>
        </div>
        <hr />
        <div class="ibox-content">
            <div class="table-responsive">
                <table class="table table-striped">
                    <thead>
                        <tr>
                            <th>ID</th>
                            <th>Name </th>
                            <th>Description </th>
                            <th>URls </th>
                        </tr>
                    </thead>
                    <tbody>
                        <tr *ngFor="let user of users; let i = index" class="tbl-row-border">
                            <td>{{user.id | barcode: true}}</td>
                            <td>{{user.login}}</td>
                            <td>{{user.description}}</td>
                            <td><a href="{{user.public_members_url}}" target="_blank">{{user.public_members_url}}</a></td>                              
                        </tr>
                    </tbody>
                </table>
            </div>
        </div>           
    </div>
</div>
</div>

Result –


I hope you are enjoying with this post! Please share with you friends. Thank you!!
By Anil Singh | Rating of this article (*****)

Popular posts from this blog

39 Best Object Oriented JavaScript Interview Questions and Answers

Most Popular 37 Key Questions for JavaScript Interviews. What is Object in JavaScript? What is the Prototype object in JavaScript and how it is used? What is "this"? What is its value? Explain why "self" is needed instead of "this". What is a Closure and why are they so useful to us? Explain how to write class methods vs. instance methods. Can you explain the difference between == and ===? Can you explain the difference between call and apply? Explain why Asynchronous code is important in JavaScript? Can you please tell me a story about JavaScript performance problems? Tell me your JavaScript Naming Convention? How do you define a class and its constructor? What is Hoisted in JavaScript? What is function overloadin

List of Countries, Nationalities and their Code In Excel File

Download JSON file for this List - Click on JSON file    Countries List, Nationalities and Code Excel ID Country Country Code Nationality Person 1 UNITED KINGDOM GB British a Briton 2 ARGENTINA AR Argentinian an Argentinian 3 AUSTRALIA AU Australian an Australian 4 BAHAMAS BS Bahamian a Bahamian 5 BELGIUM BE Belgian a Belgian 6 BRAZIL BR Brazilian a Brazilian 7 CANADA CA Canadian a Canadian 8 CHINA CN Chinese a Chinese 9 COLOMBIA CO Colombian a Colombian 10 CUBA CU Cuban a Cuban 11 DOMINICAN REPUBLIC DO Dominican a Dominican 12 ECUADOR EC Ecuadorean an Ecuadorean 13 EL SALVADOR

25 Best Vue.js 2 Interview Questions and Answers

What Is Vue.js? The Vue.js is a progressive JavaScript framework and used to building the interactive user interfaces and also it’s focused on the view layer only (front end). The Vue.js is easy to integrate with other libraries and others existing projects. Vue.js is very popular for Single Page Applications developments. The Vue.js is lighter, smaller in size and so faster. It also supports the MVVM ( Model-View-ViewModel ) pattern. The Vue.js is supporting to multiple Components and libraries like - ü   Tables and data grids ü   Notifications ü   Loader ü   Calendar ü   Display time, date and age ü   Progress Bar ü   Tooltip ü   Overlay ü   Icons ü   Menu ü   Charts ü   Map ü   Pdf viewer ü   And so on The Vue.js was developed by “ Evan You ”, an Ex Google software engineer. The latest version is Vue.js 2. The Vue.js 2 is very similar to Angular because Evan You was inspired by Angular and the Vue.js 2 components looks like -

nullinjectorerror no provider for httpclient angular 17

In Angular 17 where the standalone true option is set by default, the app.config.ts file is generated in src/app/ and provideHttpClient(). We can be added to the list of providers in app.config.ts Step 1:   To provide HttpClient in a standalone app we could do this in the app.config.ts file, app.config.ts: import { ApplicationConfig } from '@angular/core'; import { provideRouter } from '@angular/router'; import { routes } from './app.routes'; import { provideClientHydration } from '@angular/platform-browser'; //This (provideHttpClient) will help us to resolve the issue  import {provideHttpClient} from '@angular/common/http'; export const appConfig: ApplicationConfig = {   providers: [ provideRouter(routes),  provideClientHydration(), provideHttpClient ()      ] }; The appConfig const is used in the main.ts file, see the code, main.ts : import { bootstrapApplication } from '@angular/platform-browser'; import { appConfig } from '

React | Encryption and Decryption Data/Text using CryptoJs

To encrypt and decrypt data, simply use encrypt () and decrypt () function from an instance of crypto-js. Node.js (Install) Requirements: 1.       Node.js 2.       npm (Node.js package manager) 3.       npm install crypto-js npm   install   crypto - js Usage - Step 1 - Import var   CryptoJS  =  require ( "crypto-js" ); Step 2 - Encrypt    // Encrypt    var   ciphertext  =  CryptoJS . AES . encrypt ( JSON . stringify ( data ),  'my-secret-key@123' ). toString (); Step 3 -Decrypt    // Decrypt    var   bytes  =  CryptoJS . AES . decrypt ( ciphertext ,  'my-secret-key@123' );    var   decryptedData  =  JSON . parse ( bytes . toString ( CryptoJS . enc . Utf8 )); As an Example,   import   React   from   'react' ; import   './App.css' ; //Including all libraries, for access to extra methods. var   CryptoJS  =  require ( "crypto-js" ); function   App () {    var   data