JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id="textarea" rows="8" cols="40">Insertion order:
foo, bar, baz, 3, 2, 1
    
Enumeration order:
</textarea>

JavaScript

var a = {"foo":"bar", "bar":"foo", "baz":"baz", "3":3, "2":2, "1":1};
var $textarea = $("#textarea");
var keys = [];

$.each(a, function(key, value) {
    keys.push(key);
});

$textarea.append(keys.join(', ') + "\n\n");

$textarea.append("Deleting and replacing bar:\n")

delete a.bar;
a.bar = "foo";
keys = [];

$.each(a, function(key, value) {
    keys.push(key);
});

$textarea.append(keys.join(', '));