javascript - How does the comma operator work in js?

Question

I'm trying to understand how the comma operator (,) works in JavaScript, it seems to have a different behaviour when it's not put between parenthesis.

Can someone explain me why ?

Exemple for reference :

var a = 1; 
var b = 2; 
var c = (a,b);
console.log(c);
//output : as expected 
var c = a,b;
console.log(c);
//output : 1 

Answer 1

var c = (a,b);

The above uses the comma operator. It evaluates as the value of its right-hand side (i.e. b).

---

var c = a,b;

This does not use the comma operator.

The comma character here forms part of the var expression which takes a comma-separated list of variables to create in the current scope, each of which can have an optional assignment.

It is equivalent to:

var c = a;
var b;