What's the difference between static method inside a class and a function outside of it (JavaScript)

Question

I don't really catch what is the purpose of putting a static method into a class and then calling it with this class instead of just creating a function with the same code.

class test {
    static sum(a,b){
        return (a+b)
    }
}
sum = (a,b) => a+b
console.log(sum(10,5)) //15
console.log(test.sum(10,5)) //15

What is the difference? And why do people use static classes?

Answer 1

There's indeed no real technical difference between a standalone function and a static method on a class. You should not unnecessarily wrap your functions in a class, if there's no difference.

However, it can be advantageous for comprehensibility. For example, the builtin Date class has a few static methods, like Date.now. This clearly makes sense to have on the Date class, since it's very Date related. If it wasn't a static method on Date, it'd be a global function, which would need to be named something useful and which shouldn't clash with other global names. Just naming it now would probably take up a valuable global name and lead to confusion or clashes. Compare:

let foo = now();
let bar = Date.now();

Date.now is much clearer here and also doesn't take up another global name.

---

Now (pun intended), ES6 modules somewhat solve this problem, as it gives you another tool to group related functionality: modules. With modules, you can simply export a standalone function and a separate class from your module, and the caller can use it as they please:

import { now, Date } from 'hypothetical-date';

let foo = now();
let bar = new Date;

// or

import hdate from 'hypothetical-date';

let foo = hdate.now();
let bar = new hdate.Date;