Error when trying to drive 360° servo

I changed your code a bit, and now everything works as foreseen. Here is my complete test

//var Servo = require('servo').connect(C7, { range:2 });


function Servo_connect (pin,options) {
  var interval, currentPos;
  var offs = 1, mul = 1;
  if (options && options.range) {
    mul = options.range;
    offs = 1.5-(mul/2);
  }

  return {move:function(pos, time, callback) {
    if (typeof time === 'function') {
      callback = time; time = undefined;
    }
    if (typeof time !== 'number') time = 1000;
    
    var amt = 0;
    if (currentPos===undefined) currentPos = pos;
    if (interval)
      clearInterval(interval);
    var initial = currentPos;
    interval = setInterval(function() {
      currentPos = pos*amt + initial*(1-amt);
      digitalPulse(pin, 1, offs+E.clip(currentPos,0,1)*mul);

      if (amt >= 1) {
        clearInterval(interval);
        interval = undefined;
        if (callback) callback();
        return;
      } else {
        amt += 1000.0 / (20*time);
      }
    }, 20);
  }};
}


let Servo = Servo_connect(C7, { range:2 });

let Count = 0;
function move () {
  if (Count < 10) {
    Count++;
print('Count: ' + Count);
    Servo.move(1, 1000, move);
  }
}
move();

Since you clearInterval, an explicit return is not necessary, but it may be a good idea to restrict time to values > 0 in order to avoid a division by zero (or negative values)