JSFiddle - React, Tailwind, and code Playground

HTML

<div id="out"></div>

JavaScript

var friends = [
    {
        name: 'Bill Z',
       firstName: "Bill",
       lastName: "X",
       number: "999",
    },
    {
        name: 'Sam Y',
       firstName: "Sam",
       lastName: "Y",
       number: "999",
    }    
];

function getFriend(prop, value) {
    return friends.filter(function (obj) {
      return obj[prop] === value
    });
}

function listFriends() {
    var html = '';
    for (var i = 0, l = friends.length; i < l; i++) {
        html += '<b>' + friends[i].firstName + '</b><br/>';
        for (var p in friends[i]) {
            html += p.toUpperCase() + ': ' + friends[i][p] + '<br/>';
        }
    }
    return html;
}

//console.log(getFriend('firstName', 'Sam'))
document.getElementById('out').innerHTML = listFriends();