simple_client.js

const {
    OPCUAClient,
    AttributeIds,
    ClientSubscription,
    TimestampsToReturn
} = require("node-opcua");
const async = require("async");

const client = OPCUAClient.create({ endpoint_must_exist: false });

const endpointUrl = "opc.tcp://opcuademo.sterfive.com:26543";
const nodeId = "ns=7;s=Scalar_Simulation_Double";

/** @type ClientSession */
let theSession = null;

/** @type ClientSubscription */
let theSubscription = null;
async.series([


    // step 1 : connect to
    function(callback) {

        client.connect(endpointUrl, function(err) {

            if (err) {
                console.log(" cannot connect to endpoint :", endpointUrl);
            } else {
                console.log("connected !");
            }
            callback(err);
        });
    },
    // step 2 : createSession
    function(callback) {
        client.createSession(function(err, session) {
            if (!err) {
                theSession = session;
            }
            callback(err);
        });

    },
    // step 3 : browse
    function(callback) {

        theSession.browse("RootFolder", function(err, browse_result) {
            if (!err) {
                browse_result.references.forEach(function(reference) {
                    console.log(reference.browseName);
                });
            }
            callback(err);
        });
    },
    // step 4 : read a variable
    function(callback) {
        theSession.read({
            nodeId,
            attributeId: AttributeIds.Value
        }, (err, dataValue) => {
            if (!err) {
                console.log(" read value = ", dataValue.toString());
            }
            callback(err);
        })
    },

    // step 5: install a subscription and monitored item
    //
    // -----------------------------------------
    // create subscription
    function(callback) {

        theSession.createSubscription2({
            requestedPublishingInterval: 1000,
            requestedLifetimeCount: 1000,
            requestedMaxKeepAliveCount: 20,
            maxNotificationsPerPublish: 10,
            publishingEnabled: true,
            priority: 10
        }, function(err, subscription) {
            if (err) { return callback(err); }
            theSubscription = subscription;

            theSubscription.on("keepalive", function() {
                console.log("keepalive");
            }).on("terminated", function() {
            });
            callback();
        });

    }, function(callback) {
        // install monitored item
        //
        theSubscription.monitor({
            nodeId,
            attributeId: AttributeIds.Value
        },
            {
                samplingInterval: 100,
                discardOldest: true,
                queueSize: 10
            }, TimestampsToReturn.Both,
            (err, monitoredItem) => {
                console.log("-------------------------------------");
                monitoredItem
                    .on("changed", function(value) {
                        console.log(" New Value = ", value.toString());
                    })
                    .on("err", (err) => {
                        console.log("MonitoredItem err =", err.message);
                    });
                callback(err);

            });
    }, function(callback) {
        console.log("Waiting 5 seconds")
        setTimeout(() => {
            theSubscription.terminate();
            callback();
        }, 5000);
    }, function(callback) {
        console.log(" closing session");
        theSession.close(function(err) {
            console.log(" session closed");
            callback();
        });
    },

],
    function(err) {
        if (err) {
            console.log(" failure ", err);
            process.exit(0);
        } else {
            console.log("done!");
        }
        client.disconnect(function() { });
    });