Tutorial

Creating Custom Pipes in Angular

Angular

While this tutorial has content that we believe is of great benefit to our community, we have not yet tested or edited it to ensure you have an error-free learning experience. It's on our list, and we're working on it! You can help us out by using the "report an issue" button at the bottom of the tutorial.

Pipes in Angular 2+ are a great way to transform and format data right from your templates. Out of the box you get pipes for dates, currency, percentage and character cases, but you can also easily define custom pipes of your own. Here for example we create a pipe that takes a string and reverses the order of the letters. Here’s the code that would go into a reverse-str.pipe.ts file inside of your app folder:

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


Then you’d include the custom pipe as a declaration in your app module:

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { FormsModule } from '@angular/forms';
import { HttpModule } from '@angular/http';

import { AppComponent } from './app.component';
import { ReverseStr } from './reverse-str.pipe.ts';

And finally in your templates this is how you would use this custom pipe:

{{ user.name | reverseStr }}

Pipe with parameters

You can also define any amount of parameters in the pipe, which enables you to pass parameters to it. For example, here’s a pipe that adds a string before and after our provided string:

@Pipe({name: 'uselessPipe'})
export class uselessPipe implements PipeTransform {
  transform(value: string, before: string, after: string): string {
    let newStr = `${before} ${value} ${after}`;
    return newStr;
  }
}

And you would call it like that:

{{ user.name | uselessPipe:"Mr.":"the great" }}

Notice how we used ES6’s string interpolation to construct the new string with such ease: `${before} ${value} ${after}`

Creative Commons License