JSFiddle - React, Tailwind, and code Playground

HTML

<div class='result' id="result"><b>Test 1</b></div>
<div class='result' id="result2"><b>Test 2</b></div>
<div class='result' id="result3"><b>Test 3</b></div>

CSS

.result {
    margin-bottom: 20px;
}

JavaScript

var markers = [];
markers[6] = '6';
markers[7] = '7';
markers[8] = '8';


// TEST 1
for(var i = 0; i < markers.length; i++) {
    $('#result').append('<div>' + markers[i] + '</div>');
}

// TEST 2
for(var i = 0; i < markers.length; i++) {
    if(typeof(markers[i]) != 'undefined')
        $('#result2').append('<div>' + markers[i] + '</div>');
}


// TEST 3
Object.size = function(obj) {
    var size = 0, key;
    for (key in obj) {
        if (obj.hasOwnProperty(key)) size++;
    }
    return size;
};
    
var pins= {};
pins[6] = '6';
pins[7] = '7';
pins[8] = '8';

$('#result3').append('<div>Size: ' + Object.size(pins) + '</div>');
for(var i = 0; i < Object.size(pins); i++) {
    $('#result3').append('<div>' + pins[i] + '</div>');
}