JSFiddle - React, Tailwind, and code Playground

HTML

<body />

CSS

body {font-family: monospace;}

h2 {font-size: 1.5em; margin-top: 10px; font-weight: bold;}

strong {font-weight: bold;}
strong:after {content: ': ';}

JavaScript

window.obj = {
    a: 'foo',
    b: 'bar'
};

window.putHeader = function(h) {
    var header = $('<h2 />').text(h);
    $('body').append(header);
}
    
window.describeKeyValuePair = function(k,v){
    var key = $('<strong />').text('' + k);
    var value = $('<span />').text('' + v);
    var p = $('<p />').append(key).append(value);
    $('body').append(p);
};

window.putHeader('Initial obj dump');
$.each(window.obj, window.describeKeyValuePair);

window.putHeader('Value of obj.a');
$('body').append($('<p />').text('' + window.obj.a));

window.putHeader('Setting obj.a to undefined...');
window.obj.a = undefined;

window.putHeader('Initial obj dump');
$.each(window.obj, window.describeKeyValuePair);

window.putHeader('Value of obj.a');
$('body').append($('<p />').text('' + window.obj.a));