Read a value from an OPC UA server in Node.js

The code

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

(async () => {
  const client = OPCUAClient.create({ endpointMustExist: false });
  await client.connect("opc.tcp://opcua.umati.app:4840");
  const session = await client.createSession();

  const dv = await session.read(
    { nodeId: "i=2258", attributeId: AttributeIds.Value },
    TimestampsToReturn.Both
  );

  console.log("value           :", dv.value.value);
  console.log("dataType        :", dv.value.dataType);
  console.log("status          :", dv.statusCode.toString());
  console.log("source timestamp:", dv.sourceTimestamp);
  console.log("server timestamp:", dv.serverTimestamp);

  await session.close();
  await client.disconnect();
})();

What it prints

value           : 2026-09-08T03:44:59.321Z
dataType        : 13
status          : Good (0x00000000)
source timestamp: 2026-09-08T03:44:59.321Z
server timestamp: 2026-09-08T03:44:59.321Z

Notes

• Ask for TimestampsToReturn.Both while developing, then narrow it. Some PLC-embedded servers populate only ServerTimestamp meaningfully, and you want to discover that early.
• Reads take arrays. One request for two hundred nodes beats two hundred requests, up to the server's operation limit.
• Resolve namespaces with `nsu=` node id syntax or by reading the namespace array, rather than hardcoding `ns=4` and having it shift after a program download.
• Branch on `dv.statusCode.isGood()`. An Uncertain status is a real signal, not a rounding error.

What breaks first

Last verified 7 September 2026 against OPC UA 1.05.07. OPC UA Connect is an educational resource and is not affiliated with the OPC Foundation.