Searched for "javascript performance tips"

https://www.keycdn.com/blog/javascript-performance

Interesting points are

HTTP/2 uses multiplexing, therefore allowing multiple requests and responses to be sent at the same time.

Use a compression method such as Gzip or Brotli to reduce the size of your JavaScript files.

This thing:

var Person = Object.create({
	init: function(name) {
		this.name = name;
	},
	do: function(callback) {
		callback.apply(this);
	}
});

var bob = new Person('bob');

bob.do(function() {
	alert(this.name); // 'bob' is alerted because 'this' was rewired
});

This thing, though I prefer to keep the necessary javascript right in the html:

// load example.js without interrupting your webpage's rendering
<script src="example.js" async></script>
// load example.js after the page has finished loading
<script src="example.js" defer></script>

Animate with requestAnimationFrame