JavaScript Functions Are Objects

It may surprise you but it’s right there in function’s definition:

The Function object provides methods for functions. In JavaScript, every function is actually a Function object.

An example

For example, functions can have properties, just like objects:

function hello(name) {
	if (!hello.names) {
		hello.names = new Set([name]);
	} else {
		hello.names.add(name);
	}
	return `Hello, ${name}!`;
}

hello('Sue');
hello('Beth');
hello('Tom');

console.log(hello.names); // {"Sue","Beth","Tom"}

Just because you can doesn’t mean you should

This is a neat party trick but I don’t think it’s a good idea.

Code clarity is everything and this pattern gets messy quickly. It is a fun trick though!

Deep dive

Checkout Kyle Simpson’s discussion of functions in his You Don’t Know JS series.