Im trying to figure out the scaling of the value i get from a modbus read node, and ended up doing it the hard way. So i need to convert the 4 bytes from the buffer, to decimal value in a function node. This way i can easily tweak the scaling and modbus parameters manually.

I thought the easiest way would be:

Bytes -> Bits -> (apply different parameters) -> Decimal value -> apply optional scaling

And thats what i tried making, but it does not work and i dont se why. Either it does nothing(outputs NaN), or node-red just stops running. And i have to disable the flow from the node-red files. Then restart the raspberry pi, then manually start node-red again.

var In = msg.buffer;
var i;
var j;
var Bit;
var Bits = [0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0];
var BitVal8 = [128,64,32,16,8,4,2,1]
var BitVal32 = [1,2,4,8,16,32,64,128]
var Negative;
var Out;

//Sjekker om MSB er 1
if (In[0] >= 128)
{
    Negative= true;
    In[0] -= 128;
}

//Regner ut verdien av hvert bit i et 32 bit word
for (i= 8; i<32;i++)
{
    j = i-1;
    BitVal32[i]= (BitVal32[j]*2);
}

//Går gjennom alle 4 bytes (0-3)
for (i= 0; i<4; i++)
{
    //Går gjennom alle bits (0-7) og legger de inn rett i 32 bit var
    for (j=0; j<8; j++)
    {
        Bit= (j+1)*(i+1)-1;
        
        if ((In[i]/BitVal8[j])>1)
        {
            In[i]-= BitVal8[j];
            Bits[Bit]=1;
        }
    }
}

//Konverterer 32 bit var til decimal var
for (i = 0; i < 32; i++)
{
    if (Bits[i]==1)
    {
        Out+=BitVal32[i];
    }
}

//Hvis MSB var 1, negates tallet
if (Negative)
{
    Out= Out*-1;
}


msg.payload = Out;

node.status({fill:"blue",shape:"ring",text:msg.topic + ": " + msg.payload});    

return msg;

I used these nodes for a while. But i cant get them to work with certain variables from the modbus unit. Becuse the modbus parameter is different on them.

Read through this page, but its the opposite of what i want to do and i dont understand it well enough to apply it to my situation.