An Angular pipe is a feature that allows you to transform data in your templates. It takes in data as input and returns the transformed data to display. Pipes are denoted by the | symbol in Angular templates.
What are pipes in Angular?
Angular, a popular TypeScript-based web application framework, offers powerful tools for data transformation and display. Among these tools, pipes stand out as essential features for manipulating data in templates. Let’s explore Angular pipes, their functionality, and how they can enhance the development process.
Key takeaways:
Angular pipes are powerful tools for data transformation in templates.
Built-in pipes cover common scenarios like date formatting and number transformations.
Custom pipes can be created for specific transformation needs.
Pipe chaining allows for multiple transformations in sequence.
Understanding the difference between pure and impure pipes is crucial for performance optimization.
Introduction to Angular pipe
Angular pipes provide a sophisticated way to perform the tasks within the templates. They are simple functions that accept an input value and return a transformed output. Pipes make the code structured and clean. They provide a way to declare display-value transformations in the HTML template. Pipes are useful for formatting data such as dates, currency, percentages, and more.
The primary purpose of the pipes is the transformation of an existing value and reusability.
Angular pipe
How pipes work in Angular
Pipes in Angular work by taking in data as input and producing a formatted output. They are denoted by the pipe symbol (|) in Angular templates. The basic syntax for using a pipe is:
{{ value | pipeName:parameter1:parameter2 }}
Here, value is the input data, pipeName is the name of the pipe, and parameter1 and parameter2 are optional parameters that can be passed to the pipe.
Built-in pipes in Angular
Angular provides several built-in pipes for common data transformations:
Pipe | Description | Example |
| Formats dates according to locale rules |
|
| Transforms text to uppercase |
|
| Transforms text to lowercase |
|
| Transforms a number into a currency string |
|
| Transforms a number into a string with decimal points |
|
| Transforms a number into a percentage string |
|
| Converts a value into a JSON-formatted string |
|
| Creates a subset of an array or string |
|
| Unwraps a value from an asynchronous primitive |
|
| Transforms text to title case |
|
| Transforms an Object or Map into an array of key-value pairs |
|
Let’s look at an example.
Example: Date pipe
Suppose we have a pipe that computes age from a given date input, as shown in the image below.
Angular pipe
Let’s see the date example in the code as well to get a better understanding.
import { NgModule } from '@angular/core';
import { Routes, RouterModule } from '@angular/router';
const routes: Routes = [];
@NgModule({
imports: [RouterModule.forRoot(routes)],
exports: [RouterModule]
})
export class AppRoutingModule { }
Code example of a Date pipe in Angular
In the above code:
Line 8: We apply the
datepipe to the Date objectday.
Creating custom pipes
We can create custom pipes to perform specific data transformations. To create a custom pipe:
Use the
@Pipedecorator to define the pipe metadata.Implement the
PipeTransforminterface.Override the
transformmethod to define the pipe’s functionality.
Example of a custom pipe:
import { Pipe, PipeTransform } from '@angular/core';@Pipe({name: 'exponential'})export class ExponentialPipe implements PipeTransform {transform(value: number, exponent = 1): number {return Math.pow(value, exponent);}}
Creating custom pipes in Angular
Pipe chaining in Angular
Angular allows multiple pipes to be chained together, applying transformations in sequence. This is done by using multiple pipe symbols:
{{ value | pipe1 | pipe2 | pipe3 }}
What if we want the output in uppercase? We can think of it like this:
Pipe chaining in Angular
Let’s see the uppercase date example in the code as well to get a better understanding.
import { NgModule } from '@angular/core';
import { Routes, RouterModule } from '@angular/router';
const routes: Routes = [];
@NgModule({
imports: [RouterModule.forRoot(routes)],
exports: [RouterModule]
})
export class AppRoutingModule { }
Example of chain pipes in Angular
In the above code:
Line 8: We apply the
datepipe anduppercasepipe using pipe chaining to the Date objectday.
Pure vs. impure pipes
Angular pipes can be categorized as pure or impure:
Pure Pipes: Execute only when the input value changes. They are more performant and are the default type.
Impure Pipes: Can execute on every change detection cycle. They are less performant but necessary for certain scenarios.
To create an impure pipe, set pure: false in the pipe decorator:
@Pipe({name: 'myImpurePipe',pure: false})
Creating impure pipe in Angular
Best practices for using pipes
Here are some best practices we must follow:
Use built-in pipes whenever possible.
Create custom pipes for reusable transformations.
Prefer pure pipes for better performance.
Use pipe chaining judiciously to avoid complexity.
Consider using pipes for simple transformations in templates.
Conclusion
Angular pipes are a powerful and essential feature of the Angular framework. It provides tools for data transformation and formatting. From built-in pipes that handle common transformations like date formatting and number manipulation to the flexibility of creating custom pipes for specific needs, Angular’s pipe system proves to be a versatile solution for many data presentation challenges. Remember that effective use of pipes can significantly improve the code’s clarity and maintainability.
Frequently asked questions
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