Angular Pipe: A Complete Guide

Are you aiming to enhance user experience, optimise performance, or simply make your codebase more elegant? If yes, then Angular Pipes can offer an essential toolkit for achieving these goals. 

Angular Pipes serve as a bridge between your data and its representation, allowing you to tweak and present information in a way that resonates with your users. So, if you want to format dates elegantly or even chain complex transformations, this feature can be your go-to support. 

Want to know how this work and how can it benefit you? Read this blog to learn about Angular Pipe and its key features. Also, explore its various types, benefits and key components. 

Table of Contents 

1) Understanding what is Angular Pipe 

     a) Features of an Angular Pipe 

     b) Parameters of an Angular Pipe 

     c) Angular Pipe chaining 

2) Looking at the types of Pipes in Angular 

    a) Built-in Angular Pipe 

    b) Custom Angular Pipe 

    c) Pure and Impure Angular Pipe 

3) Conclusion 

Understanding what is an Angular Pipe 

An Angular Pipe is a unique feature within the Angular framework, a well-known platform for building web applications. In simple terms, an Angular Pipe takes in data and transforms it into a desired format. Imagine pouring a raw mixture into a funnel, and it emerges on the other side, refined and ready to use. That's what it does to your data. 

This transformation can be anything from formatting a date, converting a number into a currency format, changing text cases, or even implementing more complex custom transformations defined by the developer. Angular Pipes can be applied directly within the template HTML, allowing for real-time changes that respond to alterations in the underlying data. 

Moreover, the Angular framework provides several built-in pipes for common tasks, but developers have the freedom to create custom pipes tailored to their specific needs. Using them, one can keep the component code clean and focused on logic while the presentation layer handles the data formatting. 

Furthermore, this separation of concerns is part of what makes Angular Forms such an efficient and effective tool in web development. They enhance readability and maintainability, offering a more user-friendly interface for the end-user.

 

Features of an Angular Pipe 

Here are the various features of an Angular Pipe, described in the list below: 

a) Built-in pipes: Angular has a collection of pre-defined pipes for common data transformations, like dates, numbers, and strings. 

b) Custom pipes: Developers can create custom pipes, offering complete flexibility to address unique project requirements. 

c) Chaining of pipes: Multiple pipes can be linked together, allowing sequential data transformations. 

d) Pure and Impure Pipes: 

1) Pure Pipes: These are the default pipes that execute only when a pure change to the input value is detected. 

2) Impure Pipes: These execute on every component change detection cycle, providing more dynamic but potentially performance-intensive transformations. 

e) Asynchronous pipes: Angular supports asynchronous operations within pipes, allowing for tasks like fetching data from a server. 

f) Parameterisation: Pipes can take arguments or parameters for more refined control over the transformation process. 

g) Integration with HTML templates: Pipes can be directly used within HTML templates, offering a concise and clean way to apply transformations. 

h) Real-time data binding: They enable real-time data binding. It means that transformations are automatically updated if the underlying data changes. 

i) Stateless transformation: Every time a pipe receives a request, it executes the transformation as if it’s the first time. This ensures that there are no hidden dependencies or states that might affect the output. 

j) Enhanced readability: By handling transformations within the template, Angular Pipes promote cleaner and more understandable component code. 

k) Reusability: Custom pipes can be defined once and used across various components within the application, promoting code reusability. 

l) Performance optimisation: With the ability to control when pipes execute (through the distinction between pure and impure pipes), developers have tools at their disposal to optimise performance. 

m) Error handling: Properly implemented pipes can include error handling mechanisms to gracefully deal with unexpected input values or transformation issues. 

n) Localisation: Pipes like the date and currency pipes can adapt to different locales. This ensures proper formatting for various regions and cultures. 

o) Testing: Custom pipes can be independently tested, making it easy to fix any issues 

Parameters of Angular Pipe 

The parameters of Angular Pipe are many and allow for further control and customisation of data transformations. They are listed as follows:
 

a) Value parameter: The primary input for a pipe. It's the original data that you want to transform. 

b) Transform method parameter: Pipes often include a transform method that can take additional parameters to guide the transformation. These parameters are optional and defined by the developer in custom pipes or the specific built-in pipe being used. 

c) Format parameter: Used in date, currency, and number pipes. They dictate the specific format that the output should take. 

d) Locale parameter: Relevant for date and currency pipes. These allow the pipe to adapt to different regional or cultural formatting rules. 

e) Currency code parameter: Utilised in the currency pipe. Currency and code parameters specify the currency symbol or code to be used (e.g., 'GBP' for British Pounds). 

f) Digit information parameter: Found in number, currency, and percentage pipes. These often allow control over the number of integer and decimal digits, as well as the minimum and maximum fraction digits. 

g) Time zone parameter: Used in the date pipe to adjust the displayed time based on a specific time zone. 

h) Case parameter: Utilised in the lowercase and uppercase pipes. Case parameters dictate whether the text should be transformed to lower or upper case. 

i) JsonPipe parameter: Used to format an object as JSON text. They can include options like spacing to format the output. 

j) SlicePipe parameter: Allow defining where the slice should start and end and can be used on strings and arrays. 

k) Custom pipe parameter: For developer-defined custom pipes, any number of parameters can be defined. They allow the developer to create intricate transformations tailored to specific needs. 

k) Asynchronous parameter: Some pipes operate asynchronously and may include parameters related to that async operation. 

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Angular Pipe chaining 

Angular Pipe chaining is a powerful feature that allows multiple pipes to be linked together in a sequence, each taking the output of the previous one as its input. This facilitates a series of transformations on the data, creating a chain-like effect. Here are the various aspects of Angular Pipe chaining described as follows: 

a) How to implement Pipe chaining: Use the pipe symbol | between each pipe in the chain. Example: {{ value | pipe1 | pipe2:parameter }}. 

b) Built-in Pipe chaining: Angular's built-in pipes can be easily combined. Example: A date pipe can be followed by an uppercase pipe. 

c) Custom Pipe chaining: Custom pipes created by developers can be included in chains. Custom pipes allow highly bespoke transformation sequences. 

d) Parameter used in chaining: Each pipe in the chain can accept its specific parameters. They enable fine-tuned control over each step of the transformation. 

e) Order matters in chaining: The sequence of pipes determines the final result. However, changing the order may lead to a different output. 

f) Error handling in chaining: Proper error handling should be considered. It is because a failure in one pipe can affect the entire chain. 

g) Performance considerations: Chaining multiple pipes might impact performance. So, it's important to test and optimise as needed. 

h) Real-world applications of Pipe chaining: Formatting data for display, such as converting a date to a specific format and then localising it. Also, transforming data to meet business logic requirements. 

i) Chaining pure and impure Pipes: Both pure and impure pipes can be part of a chain. Thus, understanding how these different types interact is key to optimal performance. 

j) Testing Pipe chains: Rigorous testing ensures that the chain behaves as expected. Moreover, individual testing of each pipe helps in isolating issues. 

k) Debugging Pipe chains: Proper debugging techniques are required for complex chains. Thus, understanding the input and output at each stage helps in troubleshooting. 

l) Readability and maintainability: Keeping chains understandable and well-documented aids in future maintenance. Overly complex chains may become difficult to manage. 

Looking at the types of Pipes in Angular 

Pipes in Angular are of three key categories, described as follows
 

Built-in Angular Pipe 

Built-in Angular Pipes are readily available transformations that come out of the box with the Angular framework. They are designed to cater to common data transformation needs, offering a convenient and quick solution for developers.  

Examples of Built-in Pipes include the DatePipe for formatting dates, CurrencyPipe for currency conversions, and PercentPipe for handling percentages. These are engineered to adhere to standard requirements. As a result, they provide a reliable way to manipulate data without needing to write any custom code. 

Moreover, Built-in Pipes help in maintaining consistency across applications and can save considerable development time. They can also be combined with other pipes, including custom ones, to create more complex transformations. 

A common example of a built-in Angular Pipe is the DatePipe, which allows you to format dates in various ways. Here's a short code snippet that demonstrates how to use this pipe within an Angular component template: 

The current date is: {{ currentDate | date:'fullDate' }}

Example (typescript) 

@Component({ 

  selector: 'app-date-example', 

  templateUrl: './date-example.component.html', 

}) 

export class DateExampleComponent { 

  currentDate = new Date(); 

} 

Output 
“The current date is: Monday, 14 August 2023” 

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Custom Angular Pipe 

While the Built-in Pipes cover many typical use cases, there are situations when a more tailored approach is needed. This is where Custom Angular Pipes come into play. Custom pipes allow developers to define their own transformation logic based on specific project requirements.  

By creating a class with the @Pipe decorator and implementing the PipeTransform interface, developers can craft custom pipes that handle unique data manipulation tasks. Custom pipes offer a level of flexibility that enables the creation of highly bespoke solutions tailored to fit the needs of the application. Moreover, they can be reused across different components or even different projects, enhancing code maintainability and consistency. 

Example (typescript) 
You'll need to define the custom pipe by creating a new TypeScript file: 

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

@Pipe({ 

  name: 'reverseString' 

}) 

export class ReverseStringPipe implements PipeTransform { 

  transform(value: string): string { 

    return value.split('').reverse().join(''); 

  } 

} 

Next, you'll need to register the pipe in your module: 

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

import { ReverseStringPipe } from './reverse-string.pipe'; 

@NgModule({ 

  declarations: [ 

    ReverseStringPipe 

  ], 

  exports: [ 

    ReverseStringPipe 

  ] 

}) 

export class SharedModule { } 

Once the custom pipe is defined and registered, you can use it within your component templates like so: 

Original text: {{ originalText }}

Reversed text: {{ originalText | reverseString }

Assuming that originalText is a property in your component with the value "Angular", the output of this template would be: 

“Original text: Angular” 

“Reversed text: ralugnA” 

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Pure and Impure Angular Pipe 

Angular Pipes are further categorised into two types: Pure and Impure. This distinction is based on how and when the pipes execute their transformation logic. 

a) Pure Angular Pipe: Pure pipes are the default in Angular. They only execute when there is a pure change to the input value, such as a change in a primitive input value (like a string or number) or a changed object reference (like an array or object). Since pure pipes only react to actual changes, they are typically more performance efficient. THEY are especially helpful in large applications where unnecessary recalculations could lead to performance bottlenecks. 

b) Impure Angular Pipe: Impure pipes, on the other hand, execute on every component change detection cycle, regardless of whether the input data has changed or not. This makes them more dynamic but can lead to potential performance issues if not handled with care. Impure pipes are suitable for situations where constant monitoring of data changes is needed, such as when working with live data streams. 

Conclusion 

The versatile nature of Angular Pipe, encompassing built-in, custom, pure, and impure types, reflects the flexibility and power of Angular as a whole. Similarly, using an Angular Directive can streamline development by encapsulating behavior in a reusable component, providing even greater flexibility for developers in web applications.

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