index.js

const apiKey = "test_xxx";
const mollie = require("@mollie/api-client")({ apiKey });

const MANDATE_STATUS_VALID = "valid";

const retrieveCustomerMandates = customerId =>
  mollie.customers_mandates.all({ customerId });

const customerHasValidMandates = customerId => {
  return new Promise((resolve, reject) => {
    console.log(`Checking whether customer ${customerId} has valid mandates`);

    retrieveCustomerMandates(customerId)
      .then(mandates => {
        const firstValidMandate = mandates.find(
          ({ status }) => status === MANDATE_STATUS_VALID,
        );
        if (firstValidMandate) {
          resolve(firstValidMandate);
        }
        reject(`No valid mandate found for customer ${customerId}`);
      })
      .catch(error => {
        reject(error);
      });
  });
};

customerHasValidMandates("cst_pzhEvnttJ2")
  .then(mandate =>
    console.log("Found mandate for customer cst_pzhEvnttJ2", mandate),
  )
  .catch(console.log);

customerHasValidMandates("cst_UK9ArCbc2K")
  .then(mandate =>
    console.log("Found mandate for customer cst_UK9ArCbc2K", mandate),
  )
  .catch(console.log);