Pipes in Angular

Pipes in Angular are a powerful tool for processing and transforming data before presenting it in views. They can be used for tasks such as sorting, formatting and filtering data. In this article, we'll introduce pipes in Angular and how they can be used to simplify the development process.

Basic usage of pipes

1. Basic usage of pipelines In Angular, we can define a pipeline by declaring a pipeline class. For example, we can create a pipeline called "uppercase" to convert a string to uppercase:

import { Pipe, PipeTransform } from '@angular/core'; 
@Pipe({   name: 'uppercase' }) 
export class UppercasePipe implements PipeTransform {   
transform(value: string): string {     
return value.toUpperCase();  
}
}

This pipeline class implements an interface called PipeTransform, which has only one method transform, which receives a value and returns a processed value. In the above example, the transform method converts the string to uppercase.

We can use pipes in templates like this:

<h1>{
   
   { 'hello world' | uppercase }}</h1>

This will convert "hello world" to "HELLO WORLD" and render it on the page.

2. Parameters for Pipelines Pipelines can accept parameters to change their behavior as desired. For example, we can create a pipeline called "truncate" that truncates a string to a specified length. The pipeline will accept an argument specifying the length to truncate:

import { Pipe, PipeTransform } from '@angular/core'; 
@Pipe({   name: 'truncate' }) 
export class TruncatePipe implements PipeTransform {  
transform(value: string, length: number): string {    
if (value.length > length) {       
return value.substring(0, length) + '...';    
} else {      
return value;     }   } }

We can use pipes in templates, and pass parameters, like this:

<p>{
   
   { 'Lorem ipsum dolor sit amet.' | truncate: 10 }}</p>

This will truncate the string to a maximum of 10 characters and render it on the page.

3. Custom pipelines In Angular, we can easily create custom pipelines to meet specific needs. For example, we can create a pipeline called "filter" that will filter out elements from an array that match specified criteria:

import { Pipe, PipeTransform } from '@angular/core';
@Pipe({   name: 'filter' }) 
export class FilterPipe implements PipeTransform {  
transform(items: any[], field: string, value: any): any[] {   
if (!items) {    
return [];    
}     
return items.filter(item => item[field] === value); 
} 
}

We can use pipes in templates, and pass parameters, like this:

<ul>   <li *ngFor="let item of items | filter: 'type': 'fruit'">{
   
   { item.name }}</li> </ul>

This will filter out elements of type fruit from the items array.

Advanced applications of pipelines.

1. Purity of pipes In Angular, pipes are pure by default. This means that it will not recompute the output of the pipeline if the input to the pipeline does not change. This improves performance because constant data does not need to be recomputed. However, sometimes we need to recalculate the output of the pipeline in each change detection cycle, then we can use the "pure: false" option, for example:

@Pipe({   name: 'customPipe',   pure: false })

1. Asynchronous Pipelines Sometimes, we need to fetch data asynchronously and then process the data in a pipeline. In this case, we can use RxJS's Observable and pipe operators. For example, we can create a pipe called "asyncPipe" that will perform some operations on data fetched asynchronously:

import { Pipe, PipeTransform } from '@angular/core';
import { Observable } from 'rxjs'; 
import { map } from 'rxjs/operators'; 
@Pipe({   name: 'asyncPipe' }) 
export class AsyncPipe implements PipeTransform {
transform(value$: Observable<any>): Observable<any> {
return value$.pipe(
map(value => {         
// do something with the value     
return transformedValue;   
})    
);  
} 
}

We can use pipes in templates and pass Observables to pipes like this:

<p>{
   
   { value$ | asyncPipe }}</p>

2. Multiple Pipelines We can perform multiple operations by chaining multiple pipelines together. For example, we can create a pipe called "datePipe" that will format a date and then truncate it to a specified length:

import { Pipe, PipeTransform } from '@angular/core'; 
import { DatePipe } from '@angular/common'; 
@Pipe({   name: 'datePipe' }) 
export class DatePipe implements PipeTransform {   
constructor(private datePipe: DatePipe) {}   
transform(value: Date, format: string, length: number): string {  
let formattedValue = this.datePipe.transform(value, format);    
if (formattedValue.length > length) {      
formattedValue = formattedValue.substring(0, length) + '...';     }   
return formattedValue;  
} }

We can use pipelines in templates and chain multiple pipelines like this:

<p>{
   
   { myDate | date: 'yyyy-MM-dd' | datePipe: 'MMM d, y': 10 }}</p>

This will format the date and truncate it to a maximum of 10 characters.

The above are some other applications and operations of Angular pipelines. Pipelines are a very powerful tool that can make our code cleaner, more maintainable, and improve performance.