.toString(radix) ?

Hello,
i'm working with Voice module from DFRobot

if i use an array of command i'm supposed to receive some datas
i'm trying to convert the data in hexa value...
when i'm trying .toString(radix), console displays always the same char, not bin or oct or hex value...

sorry, where i'm wrong?

s.setup(9600,{rx:A8, tx:B7});
  s.on('data', function(d) {
    console.log(d.toString(2),d.toString(8),­d.toString(16));
  });

it display

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