Problem with the DS18B20 temperature sensor (NUCLEO-F401RE board )

Your best bet is to find the function in the reference: http://www.espruino.com/Reference

Then there's a ⇒ symbol next to the function's title. Click on that and you go to the implementation: https://github.com/espruino/Espruino/blob/master/src/jswrap_onewire.c#L111

If you want actual specifics of the OneWire protocol, it's best just to google it.

Can you try adding this to the end of your code:

sensor.getTemp = function(callback) {
  function read(me) {
    var s = me._r();
    var temp = s[0] + (s[1]<<8);
    if (temp & 32768) temp -= 65536;
    temp = temp / ((me.type==10)?2:16);
    if (callback) callback(temp);
    return temp;
  }
  this.bus.select(this.sCode);
  this.bus.write(0x44, true);
  if (!callback) return read(this);
  var tim = {9:94, 10:188, 11:375, 12:750};
  setTimeout(read, tim[this.getRes()], this);
};

And see what it says? It'll ignore the CRC.