Why in JavaScript +(3,13) returns 13?

Question

What's going on here using JavaScript?

var c = +(3,13);    

I got c equals to 13. Why?

Answer 1

The comma functions as an expression separator operator. The value of a sequence of expressions separated by commas is the value of the last expression. Thus 3, 13 has the value 13. That's surrounded with parentheses and the unary + operator, neither of which will affect that value.

The comma operator is useful in only a small number of situations, generally involving expressions with side effects. In particular, your example is basically pointless. However, there are situations where some statement syntax allows for a single expression, so the comma operator lets you sneak in more than one.