Question

MDN claims that:

The comma operator evaluates both of its operands (from left to right)
and returns the value of the second operand.

However, when I tried running <script> alert(1, 2); </script>, it shows a “1” instead of a “2”.

Am I misunderstanding something?

Answer 1

In the context of a function call, the comma is used to separate parameters from each other. So what you’re doing is passing a second parameter to alert() which gets silently ignored.

What you want is possible this way:

 alert((1,2));

The extra brackets form a parameter on their own; inside them you can use the comma as an operator.