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.

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

@Component({
  selector: 'app-root',
  template: `
    <div>
      <p *ngFor="let f of fileSizes">{{ f | formatFileSize }}</p>
      <p>{{ largeFileSize | formatFileSize:true }}</p>
    </div>`
})
export class AppComponent {
  fileSizes = [10, 100, 1000, 10000, 100000, 10000000, 10000000000];
  largeFileSize = Math.pow(10, 15)
}

View Example

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