Handlebars:
Template
{{firstname}} {{loud lastname}}
Preparation-Script
Handlebars.registerHelper('loud', function (aString) {
    return aString.toUpperCase()
})
Input
{
  firstname: "Yehuda",
  lastname: "Katz",
}
Output
Yehuda KATZ
Last Updated: 8/1/2019, 7:57:01 PM