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?

3. What is a pure and impure pipe?

4. What is Async Pipe?

5. How to create and use a custom pipe?

6. How to create a globally available custom“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({

})

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({

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({

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 :-

<h2>Angular 2 - User Services</h2>

</div>

<hr />

<thead>

<tr>

<th>Description </th>

</tr>

</thead>

<tbody>

<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>

Result –

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