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JavaScript convert Array of 4 bytes into a float value from modbusTCP read

rated 0 times [ 76] [ 6] / answers: 1 / hits: 17826 / 7 Years ago, thu, march 9, 2017, 12:00:00

I'am trying to convert a array of 4 bytes to a float value. Here is the thing:

I get an answer from my request via ModbusTCP, this looks something like this:

{ data: [ 16610, 40202 ], buffer: { type: Buffer, data: [ 64, 226, 157, 10 ] } }

This string is converted into a json-object, parsed and accessed with

var ModbusArray = JSON.parse(msg.payload);

var dataArray = ModbusArray.buffer.data;

(the msg.payload comes from node red)

Until here it works find. The Array represents a floating value. In this case it should be a value of around 7.0.

So, here is my Question: how can I get a float from this dataArray?

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answered 7 Years ago pierre · Accepted Answer

You could adapt the excellent answer of T.J. Crowder and use DataView#setUint8 for the given bytes.

var data =  [64, 226, 157, 10];



// Create a buffer

var buf = new ArrayBuffer(4);

// Create a data view of it

var view = new DataView(buf);



// set bytes

data.forEach(function (b, i) {

    view.setUint8(i, b);

});



// Read the bits as a float; note that by doing this, we're implicitly

// converting it from a 32-bit float into JavaScript's native 64-bit double

var num = view.getFloat32(0);

// Done

console.log(num);