GetCustomer().then(customer => {
    ProcessCustomer(customer).then(processingResult =>
    {
        console.log(customer);
        console.log(processingResult);
    });
});

GetCustomer().then(customer => {
        return Promise.all([customer, ProcessCustomer(customer)]);
    }).then(results => {
        console.log(results[0]);
        console.log(results[1]);
    });