Angular 2 Pipes

Angular 2 Pipes helps us to format or transform data to display in our template. They are similar to Filters in AngularJS. In this Tutorial, we are going to look at what is pipes are & how to use them. We will see how to pass arguments to the pipe and how to chain pipes. We are also going to look at the few list of angular 2 built-in pipes like currency pipe, date pipe, number pipe, percent pipe, decimal pipe, & slice pipe.

Angular 2 Pipes

There are many circumstances where we may have to change the appearance of the data before presenting it the user. The most common examples are dates. That is where Angular 2 Pipes comes handy. They take the data as input and transforms that data to get the desired output.

Syntax of Pipe

Expression | pipeOperator[:pipeArguments]

Where

Expression : is the expression, which you want to transform

| : is the Pipe Character

pipeOperator : name of the Pipe

pipeArguments: arguments to the Pipe

Using the Pipes

In this example let use Angular 2 built in date pipe to transform the date

Component class

import { Component } from '@angular/core';
import { FormsModule } from '@angular/forms';

@Component({
    selector: 'app-root',
    templateUrl: `<p> Unformatted date : {{toDate }} </p>
                  <p> Formatted date : {{toDate | date}} </p>` 
}) 
export class AppComponent 
{ 
    title: string = 'pipe Example' ; 
    toDate: Date = new Date(); 
}

In the above example, we are taking current date and transforming it into the easily readable format using the date pipe. We have included the unformatted date format for comparison. The output is as shown below

Passing arguments

We can also pass optional arguments to the pipe. The arguments are added to the pipe using a colon (:) sign followed by the value of the argument. If there are multiple arguments separate each of them with the colon (:). For example date pipe accepts one optional argument called “format”. The “medium” is one of the valid value of the format argument, which displays the date in “yMMMdjms” format. The example code is as shown below.

{{toDate | date:'medium'}}

The parameter ‘medium’ displays the date as Nov 22, 2016, 10:04:10 PM

Chaining Pipes

Pipes can be chained together to make use of multiple pipes in one expression. For example in the following code, the toDate is passed to the Date Pipe. The output of Date pipe is then passed to the uppercase pipe.

toDate | date | uppercase

The Angular 2 Built-in pipes

The Angular 2 has several built-in pipes, which you can use in your application. You can read about them from this link

Some of the important pipes are Date Pipe, Uppercase Pipe, LowercasePipe, Number Pipe/Decimal Pipe, Currency Pipe, and Percent Pipe etc

DatePipe

The Date pipe formats the date according to locale rules. The syntax of the date pipe is as shown below

date_expression | date[:format]

Where

date_expression is a date object or a number

date is the name of the pipe

format is the date and time format string which indicates the format in which date/time components are displayed.

Some of the common format strings are

Format argument also supports some predefined commonly used formats

You can read about the complete list from link

Example of Datepipe

import { Component } from '@angular/core';
import { FormsModule } from '@angular/forms';
@Component({
    selector: 'app-root',
    template:`<p>medium : {{toDate | date:'medium'}} </p>
              <p>short : {{toDate | date:'short'}} </p>
              <p>fullDate : {{toDate | date:'fullDate'}} </p>
              <p>longDate : {{toDate | date:'longDate'}} </p>
              <p>mediumDate : {{toDate | date:'mediumDate'}} </p>
              <p>shortDate : {{toDate | date:'shortDate'}} </p>
              <p>mediumTime : {{toDate | date:'mediumTime'}} </p>
              <p>dd-MM-y : {{toDate | date:'dd-MM-y'}} </p>
              <p>dd-MM-yy HH:mm : {{toDate | date:'dd-MM-yy HH:mm'}} </p>`
})
export class AppComponent
{
    title: string = 'Angular 2 pipes Example' ;
    toDate: Date = new Date();
}

UpperCasePipe & LowerCasePipe

As the name suggests, these pipes transform the string to Uppercase or lowercase

import { Component } from '@angular/core';
import { FormsModule } from '@angular/forms';

@Component({
    selector: 'app-root',
    template:`<p>Unformatted :{{msg}} </p>
              <p>Uppercase :{{msg | uppercase}} </p>
              <p>Lowercase :{{msg | lowercase}} </p>`
})
export class AppComponent
{
    title: string = 'Angular 2 pipes Example' ;
    msg: string= 'Welcome to Angular 2';
}

Read more about uppercasepipe & lowercasepipe

SlicePipe

Creates a new List or String containing a subset (slice) of the string or array. This Pipe uses the JavaScript API Array.prototype.slice() and String.prototype.slice().

Syntax

array_or_string_expression | slice:start[:end]

Where

array_or_string_expression is the string to slice

slice is the name of the pipe

start is the start position/index from where the slicing will start

end is the ending index/position in the array/string

The slice pipes take two arguments. The first argument start is the starting index of the string/array. The second argument end is the ending index of the string/array. If the start or end index is negative then the index is counted from end of the string/array

Example

import { Component } from '@angular/core';
import { FormsModule } from '@angular/forms';
@Component({
    selector: 'app-root',
    template:`<p>Complete String :{{msg}} </p>
              <p>Example 1 :{{msg | slice:11:20}} </p>
              <p>Example 2 :{{msg | slice:-9}} </p>`
})

export class AppComponent
{
    title: string = 'Angular 2 pipes Example' ;
    msg: string= 'Welcome to Angular 2';
}

Both the above examples will display Angular 2. You can read more about slice from this link

DecimalPipe / NumberPipe

The Decimal Pipe is used to Format a number as Text. This pipe will format the number according to locale rules.

Syntax

number_expression | number[:digitInfo]

Where

number_expression is the number you want to format

number is the name of the pipe

digitInfo is a string which has the following format

{minIntegerDigits}.{minFractionDigits}-{maxFractionDigits}

Where

minIntegerDigits is the minimum number of integer digits to use. Defaults to 1.

minFractionDigits is the minimum number of digits after fraction. Defaults to 0.

maxFractionDigits is the maximum number of digits after fraction. Defaults to 3.

Example

import { Component } from '@angular/core';
import { FormsModule } from '@angular/forms';
@Component({
    selector: 'app-root',
    template: `<p> Unformatted :{{num}}</p>
               <p> Formatted :{{num | number}}</p>
               <p> Formatted :{{num | number:'3.1-2'}}</p>
               <p> Formatted :{{num | number:'7.1-5'}} </p>`
})

export class AppComponent
{
    title: string = 'Angular 2 pipes Example' ;
    num: number= 9542.14554;
}

PercentePipe

Formats the given number as a percentage according to locale rules.

number_expression | percent[:digitInfo]

Where

number_expression is the number you want to format

percent is the name of the pipe

digitInfo is a string which has the following format. It is similar to used in decimal pipe

Example code

import { Component } from '@angular/core';
import { FormsModule } from '@angular/forms';

@Component({
    selector: 'app-root',
    template:`<p>Unformatted :{{per}} </p>
              <p>Example 1 :{{per | percent }} </p>
              <p>Example 2 :{{per | percent:'1.2-2'}} </p>`
})
export class AppComponent
{
    title: string = 'Angular 2 pipes Example' ;
    per: number= .7414;2';
}

More about Percent pipe from the link

CurrencyPipe

Formats a number as currency using locale rules.

number_expression | currency[:currencyCode[:symbolDisplay[:digitInfo]]]

Where

number_expression currency to format a number as currency.

Currency is the name of the pipe

currencyCode is the ISO 4217 currency code, such as USD for the US dollar and EUR for the euro.

symbolDisplay is a boolean indicating whether to use the currency symbol or code. Use true to display symbol and false to use code

digitInfo is similar to the one used in decimal pipe

Example

import { Component } from '@angular/core';
import { FormsModule } from '@angular/forms';
@Component({
    selector: 'app-root',
    template: `<p>Unformatted :{{cur}} </p>
               <p>Example 1 :{{cur | currency }} </p>
               <p>Example 2 :{{cur | currency:'INR':true:'4.2-2'}} </p>`
})

export class AppComponent
{
    title: string = 'Angular 2 pipes Example' ;
    cur: number= 175;
}

Read more about the currencyPipe from the link