Angular 2: pipes - How to format a phone number?

I've searched here and there, and I am not able to find something specific about formatting a phone number.

Currently, I am retrieving phone numbers form a JSON in the following format:

25565115

However, I want to achieve this result:

02-55-65-115

For that, I believe that I need to use a custom pipe and I don't think that there is a built-in one that does it automatically.

Can you please give me some guidance on how to do so?

StackBlitz

pipe implementation in TS would look like this

import { Pipe } from "@angular/core";

@Pipe({
  name: "phone"
})
export class PhonePipe {
  transform(rawNum) {
    rawNum = rawNum.charAt(0) != 0 ? "0" + rawNum : "" + rawNum;

    let newStr = "";
    let i = 0;

    for (; i < Math.floor(rawNum.length / 2) - 1; i++) {
      newStr = newStr + rawNum.substr(i * 2, 2) + "-";
    }

    return newStr + rawNum.substr(i * 2);
  }
}

---

Declare the PhonePipe in your NgModule's declarations

---

Usage:

import {Component} from 'angular/core';

@Component({
  selector: "my-app",
  template: `
    Your Phone Number: <input [(ngModel)]="myNumber" />
    <p>
      Formatted Phone Number: <b>{{ myNumber | phone }}</b>
    </p>
  `
})
export class AppComponent {
  myNumber = "25565115";
}

There are many things that can be improved, I just made it work for this particular case.