JSFiddle - React, Tailwind, and code Playground

HTML

<p id="3"></p>
    <button onclick="ObjectArray()">click me</button>

JavaScript

function ObjectArray() {
    // object literal
    var id1 = {
        firstName: "John",
        lastName: "Doe",
        id: "12345"
    };

    // keyword new
    var id2 = new Object;
    id2.firstName = "Adam";
    id2.lastName = "Bakely";
    id2.id = "abcdef";

    // object constructor 
    function employee(first, last, id_num) {
        this.firstName = first;
        this.lastName = last;
        this.id_num = id_num;
    }
    var id3 = new employee("joe", "john", "abc123");

    //create an array
    var IdArray = [id1, id2, id3];

    //for loop to display results
    var text="";
    var i;

    for (i = 0;i < IdArray.length; i++){
        text += IdArray[i].firstName + "<br>";
    document.getElementById("3").innerHTML = text;
    }  
}