Javascript IF multiple arguments [duplicate]

I’m debugging an external js library code and I found this syntax:

if(argument1, argument2) { ... }

It is the first time I face more than one argument in an if block, what is its meaning?

I tried to understand how it works with some tests:

if(false,false,true) alert("TEST"); //this alert is fired!

and

if(true,false,false) alert("TEST"); //this alert is not fired!

And it seems only the last argument is evaluated.