An interface that is implemented by pipes in order to perform a transformation. Angular invokes the transform method with the value of a binding as the first argument, and any parameters as the second argument in list form.

interface PipeTransform {
  transform(value: any, ...args: any[]): any
}

Methods

transform()
transform(value: any, ...args: any[]): any Parameters value any args any[] Returns any

Usage notes

In the following example, TruncatePipe returns the shortened value with an added ellipses.

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

@Pipe({name: 'truncate'})
export class TruncatePipe implements PipeTransform {
  transform(value: string) {
    return value.split(' ').slice(0, 2).join(' ') + '...';
  }
}

Invoking {{ 'It was the best of times' | truncate }} in a template will produce It was....

In the following example, TruncatePipe takes parameters that sets the truncated length and the string to append with.

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

@Pipe({name: 'truncate'})
export class TruncatePipe implements PipeTransform {
  transform(value: string, length: number, symbol: string) {
    return value.split(' ').slice(0, length).join(' ') + symbol;
  }
}

Invoking {{ 'It was the best of times' | truncate:4:'....' }} in a template will produce It was the best.....