testwrite.js

const opcua = require("node-opcua");

const userName = "user1"

const password = "password1"
//xx const endpointUrl = "opc.tcp://192.168.249.31:4840";
const endpointUrl = "opc.tcp://localhost:26543";
//xx const nodeId = "ns=4;s=opctest1_Copy1";
const nodeId =  "ns=411;s=Scalar_Static_UInt16";

async function CreateConnection(){

    console.log('Trying to connect ...');
    const client = new opcua.OPCUAClient({endpoint_must_exist: false });

    await client.connect(endpointUrl);
    console.log('Connected!');

    const session = await client.createSession({userName: userName, password: password});

    let dataValue = await session.read({nodeId: nodeId })
    console.log(dataValue.toString());

    const nodeToWrite = {
        nodeId: nodeId,
        attributeId: opcua.AttributeIds.Value,
        value: /* DataValue */{
            statusCode: opcua.StatusCodes.Good,
            value: /* Variant */{
                dataType: opcua.DataType.UInt16,
                value: 1098
            }
        },
    }
    let risultato = await session.write(nodeToWrite);
    console.log(risultato.toString());

    dataValue = await session.read({nodeId: nodeId })
    console.log(dataValue.toString());

    await client.closeSession(session,true);
    await client.disconnect();
};

CreateConnection();