JSFiddle - React, Tailwind, and code Playground

JavaScript

function sayBill() {
   console.log('bill');
}

function sayHiAfterTwoSeconds(callback) {

  setTimeout(function() {
     console.log('hi');
     if (typeof callback === 'function') {
        callback();
     }
  });

}

sayHiAfterTwoSeconds(sayBill);
// will output 'hi bill'