Service para obtenção de token em Angular

Typescript
import { Injectable } from '@angular/core';
import { environment } from 'src/environments/environment';

export interface ICreditCardGerenciaNet {
brand: string;
number: string;
cvv: string;
expiration_month: string;
expiration_year: string;
}

@Injectable({
providedIn: 'root'
})
export class GerenciaNetService {
private static readonly _PAYEE_CODE = "SEU_PAYEE_CODE";
private static readonly _ENDPOINT = environment.production ? "https://api.gerencianet.com.br/v1/cdn" : "https://sandbox.gerencianet.com.br/v1/cdn";

constructor() { }

public getPaymentToken(creditCard:ICreditCardGerenciaNet) : Promise {
return new Promise((resolve, reject)=>{
var s = document.createElement('script');
s.type='text/javascript';

var v = Math.random()1000000;
s.src=${GerenciaNetService._ENDPOINT}/${GerenciaNetService._PAYEE_CODE}/${v};
s.async=false;
s.id = GerenciaNetService._PAYEE_CODE;

if(!document.getElementById(GerenciaNetService._PAYEE_CODE)){
document.getElementsByTagName('head')[0].appendChild(s);
}

window['$gn'] = {
validForm:true,
processed:false,
done:{},
ready:function(fn){
window['$gn'].done = fn;
}
};

window['$gn'].ready((checkout)=>{
checkout.getPaymentToken(creditCard, (error, response)=>{
if(error) {
reject(error);
}else{
resolve(response.data.payment_token);
}
});
});
});
}

}