New primitive
With unique IDs
Customized
Symbols were made for Metaprogramming
<!DOCTYPE html>
<html>
<head>
<script src="https://cdnjs.cloudflare.com/ajax/libs/babel-core/5.8.29/browser.js"></script>
<script type="text/babel">
const id = Symbol();
const courseInfo = {
title: "ES6",
topics: ["babel", "syntax", "functions", "classes"],
id: "js-course"
};
courseInfo[id] = 41284;
console.log(courseInfo);
</script>
<title>Symbols</title>
</head>
<body>
</body>
</html>
Source: https://www.freecodecamp.org/news/how-did-i-miss-javascript-symbols-c1f1c0e1874a/
