JSFiddle - React, Tailwind, and code Playground

HTML

<div id="output"></div>

CSS

#output{
    border:2px solid #CCC;
    padding:0.25em;
}

JavaScript

// A traveler class represents a traveler
function Traveler(firstName, lastName, phone) {
  this.firstName = firstName;
  this.lastName = lastName;
  this.phone = phone;
}

// An array to store all travelers
var travelers = new Array();

// Add Traveler
function addTraveler(traveler) {
    travelers.push(traveler);
}

// Remove Traveler (returns the removed traveler)
function removeTraveler() {
    return travelers.pop();
}

// Display Travelers
function renderTravelers() {
    var htmlList = "";
    var arrayLength = travelers.length;
    
    for (var i = 0; i < arrayLength; i++) {
        htmlList += 
            "<li>" + 
            travelers[i].firstName + " " + 
            travelers[i].lastName  + " " + 
            travelers[i].phone     +
            "</li>"
    }
    htmlList = "<ul>" + htmlList + "</ul>";
    htmlList += "<em>Number of Travelers: " + arrayLength + "</em>";
    document.getElementById("output").innerHTML += htmlList + "<hr>";
}
    
// ::MAIN::
// Add some travelers
addTraveler(new Traveler("Albert", "Einstein", "555-7331"));
addTraveler(new Traveler("Nikola", "Tesla", "555-1010"));
renderTravelers();
// --
var removed = removeTraveler();
renderTravelers();
// --
addTraveler(removed);
renderTravelers();
// --
addTraveler(new Traveler("Marie", "Curie", "555-4567"));
addTraveler(new Traveler("Isaac", "Newton", "555-9988"));
renderTravelers();
// --
var removed = removeTraveler();
var removed = removeTraveler();
var removed = removeTraveler();
var removed = removeTraveler();
renderTravelers();