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Pipes

Pipes are a very useful feature in Angular. They allow you to transform data in your HTML templates, giving you more control over how data is displayed. Pipes are simple functions you can use in template expressions to accept an input value and return a transformed value.

Basic Syntax of Pipes​

The basic syntax of a pipe in Angular looks like this:

{{ value | pipeName }}

Here, 'value' is the data that you want to transform and 'pipeName' is the name of the pipe you want to use.

For example, if we want to transform a string to uppercase, we can use Angular's built-in 'uppercase' pipe like this:

{{ 'hello world' | uppercase }} <!-- Output: HELLO WORLD -->

Built-in Pipes in Angular​

Angular provides several built-in pipes for common data transformations, including manipulating dates, numbers, strings, arrays, and objects. Some of the commonly used built-in pipes are:

  1. uppercase and lowercase Pipes: These transform text to all uppercase or all lowercase, respectively.

  2. date Pipe: This formats a date value according to locale rules.

  3. decimal Pipe: This transforms a number into a string with a decimal point, where the fraction size is provided as an argument.

  4. json Pipe: This pipe is useful for debugging purposes as it can transform an object or any value into a JSON string.

  5. slice Pipe: This creates a new array or string containing a subset of the elements.

Custom Pipes​

While Angular's built-in pipes cover a lot of common use cases, you may need to create your own custom pipes for more specific tasks. Custom pipes are created by declaring a class that implements the PipeTransform interface.

Here's an example of a simple custom pipe that doubles a number:

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

@Pipe({name: 'double'})
export class DoublePipe implements PipeTransform {
  transform(value: number): number {
    return value * 2;
  }
}

You can then use this custom pipe in your template like this:

{{ 5 | double }} <!-- Output: 10 -->

Chaining Pipes​

You can chain pipes together for more complex transformations. The output of one pipe is used as the input to the next pipe.

Here's an example of chaining pipes:

{{ 'hello world' | uppercase | slice:0:5 }} <!-- Output: HELLO -->

In this example, the text 'hello world' is first transformed to uppercase ('HELLO WORLD') and then the first five characters are extracted ('HELLO').

Conclusion​

Pipes in Angular are a powerful tool for transforming data right in your templates. They're easy to use and can be chained together for more complex transformations. Plus, with the ability to create custom pipes, you can handle any data transformation needs your application might have. Remember to always consider the performance implications when using pipes, especially in large applications.