Custom Pipes

Angular allows you to create your own custom pipes:

import { Pipe, PipeTransform } from '@angular/core';
const FILE_SIZE_UNITS = ['B', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'];
const FILE_SIZE_UNITS_LONG = ['Bytes', 'Kilobytes', 'Megabytes', 'Gigabytes', 'Pettabytes', 'Exabytes', 'Zettabytes', 'Yottabytes'];
@Pipe({
name: 'formatFileSize'
})
export class FormatFileSizePipe implements PipeTransform {
transform(sizeInBytes: number, longForm: boolean): string {
const units = longForm
? FILE_SIZE_UNITS_LONG
: FILE_SIZE_UNITS;
let power = Math.round(Math.log(sizeInBytes) / Math.log(1024));
power = Math.min(power, units.length - 1);
const size = sizeInBytes / Math.pow(1024, power); // size in new units
const formattedSize = Math.round(size * 100) / 100; // keep up to 2 decimals
const unit = units[power];
return `${formattedSize} ${unit}`;
}
}

Each custom pipe implementation must:

  • have the @Pipe decorator with pipe metadata that has a name property. This value will be used to

    call this pipe in template expressions. It must be a valid JavaScript identifier.

  • implement the PipeTransform interface's transform method. This method takes the value being piped

    and a variable number of arguments of any type and return a transformed ("piped") value.

Each colon-delimited parameter in the template maps to one method argument in the same order.

View Example