converter/src/app/native-library-wrapper.service.ts

import {Injectable} from '@angular/core';
import * as NativePunycode from 'punycode';
import * as NativeQuotedPrintable from 'quoted-printable';
import * as NativeUtf8 from 'utf8';

@Injectable({
  providedIn: 'root'
})
export class NativeLibraryWrapperService {
  public utf8: Utf8;
  public quotedPrintable: QuotedPrintable;
  public punycode: Punycode;

  constructor() {
    this.utf8 = NativeUtf8;
    this.quotedPrintable = NativeQuotedPrintable;
    this.punycode = NativePunycode;
  }
}

interface Punycode {
  encode(input: string): string;

  decode(input: string): string;
}

interface QuotedPrintable {
  encode(input: string): string;

  decode(input: string): string;
}

interface Utf8 {
  encode(input: any): string;

  decode(input: string): any;
}