rotary encoder strange behavior (too many datas)

Hello,

i'm playing with a rotary encoder a big MYSM60-100PPRR-5L with the example given
but the console is populated with too many answer for 1 step.

function onInit() {
  var step = 0;
  require("Encoder").connect(A5,A8, (dir) => {
    print(dir);
    if (dir > 0) {
      //allume la led 20ms
      digitalPulse(LED1, 1, 20);
    } else {
      digitalPulse(LED2, 1, 20);
    }
  });
}

console return for 1step backward

-1
-1
-1
-1
-1
1
> 

and

1
1
1
1
> 

for 1 step forward...

what i'm doing badly?