replace string template

/* Simple Hello World in Node.js */
let a = {link:'www.subdomain.com', requestId:'12345', userNameFormat:'US-ENGLISH'};

let mailBody = 'This is an automatic notification to let you know that the records  on #requestId# you had requested are now available for you to view #userNameFormat#. Please log in to the application by clicking the following link: #link#';

Object.keys(a).forEach(key => {
   mailBody = mailBody.replace(`#${key}#`,a[key]);
});
console.log(mailBody);