How to define and print hex/hexadecimal values in JS

tostring(10) does not work.
I'm trying to convert hex to dec, what's the problem?
My code:
print((31).toString(10)); //returns 31
print((31).toString(16)); //returns 1f

figured out th problem by myself :)
it is necessary to write so:
print((0x31).toString(10)); // returns 49