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OPC UA Client

Learn how to connect to an OPC UA server using the Heisenware OPC UA integration.

The OpcuaClient class provides a high-level interface for communicating with OPC UA servers. It simplifies complex operations like establishing secure connections, Browse the server's address space, reading and writing variables, calling methods, monitoring data for changes, and handling file transfers.

An instance of the client must be created to manage the connection state and session with a server. For secure connections, certificates must be generated first using the createCertificates function.

Video tutorial

Watch the video to learn how to connect to an OPC UA Server and read, record and visualize OPC UA data from that server within Heisenware.

createCertificates

This is a static utility function that should be run once to generate the necessary client and user certificates for establishing secure connections. It creates a local Public Key Infrastructure (PKI) folder containing the self-signed certificates and private keys required for authentication and encryption.

Parameters

None.

Example

# (No arguments needed)

Output

Returns true upon successful creation of the certificates.

create

This function creates an instance of the OPC UA client. It can be configured for either an unsecured connection or a secure connection using various security policies.

Parameters

  • options: An object to configure the client's security settings. For an unsecured connection, leave this argument empty.

    • securityMode: The security mode, can be None, Sign, or SignAndEncrypt.

    • securityPolicy: The security policy, such as Basic256Sha256, Aes128_Sha256_RsaOaep, etc.

Example: Unsecured Connection

To create a client for an unsecured connection, call create with no arguments.

# (No arguments needed)

Example: Secure Connection

This creates a client configured for a secure connection using the certificates generated by createCertificates.

# options
securityMode: SignAndEncrypt
securityPolicy: Basic256Sha256

connect

Establishes a connection to an OPC UA server endpoint and creates a session. You can connect anonymously or provide user credentials.

Parameters

  • endpointUrl: The full endpoint URL of the OPC UA server (e.g., opc.tcp://server.com:4840).

  • userIdentity: An object containing user credentials.

    • username: The user's name for password-based authentication.

    • password: The user's password.

    • useDefaultUserCertificate: Set to true to authenticate using the default user certificate generated by createCertificates.

Example: Anonymous Login

# endpointUrl
opc.tcp://milo.digitalpetri.com:62541/milo

Example: Username and Password Login

# endpointUrl
opc.tcp://my-secure-server.com:4840
# userIdentity
username: myuser
password: mysecretpassword

Example: Certificate-Based Login

This authenticates using the default user certificate.

# endpointUrl
opc.tcp://my-secure-server.com:4840
# userIdentity
useDefaultUserCertificate: true

Output

Returns true if the connection and session creation are successful.

disconnect

Closes the active session and disconnects from the OPC UA server.

Parameters

None.

Output

Returns true on a successful disconnection.

isConnected

Checks if the client has a valid and active channel with the server.

Parameters

None.

Output

Returns true if the client is connected, otherwise false.

browse

This is the generic, non-recursive browse function. It can start from any node address on the server. The more specific functions like browseObjects are convenience wrappers around this one.

Parameters

  • address: The nodeId or a full browse path (e.g., /0:Objects/2:Demo) from which to start Browse.

Example

# address
/0:Objects/2:Demo

Output

An array of objects, where each object represents a found node and contains its browseName, nodeId, and nodeClass.

browseObjects

Performs a non-recursive browse of the server's Objects folder. You can specify a deeper path to start from.

Parameters

  • path: The browse path, starting from within the Objects folder. Path items are separated by /, and each item uses namespaceIndex:BrowseName format (e.g., 2:Demo/2:Dynamic).

Example

# path
2:Demo/2:Dynamic/2:Scalar

Output

An array of objects, where each object represents a found node and contains its browseName, nodeId, and nodeClass.

browseTypes

Performs a non-recursive browse of the server's Types folder. This is useful for exploring the server's data type hierarchy.

Parameters

  • path: An optional browse path to start from within the Types folder. If omitted, it browses from the root of the Types folder.

Example

# path
0:BaseObjectType/0:FolderType

Output

An array of objects, where each object represents a found data type node.

browseViews

Performs a non-recursive browse of the server's Views folder. Views are predefined, filtered collections of nodes.

Parameters

  • path: An optional browse path to start from within the Views folder. If omitted, it browses from the root of the Views folder.

Example

# path
0:Server

Output

An array of objects, where each object represents a found node within the specified view.

readNode

Reads all attributes of a specific OPC UA node, returning a detailed data structure. This is more comprehensive than readVariable, which only fetches the node's value.

Parameters

  • address: The nodeId or a valid browse path of the node to read.

Example: Read using nodeId

# address
ns=2;s=Demo.Dynamic.Int32

Example: Read using Browse Path

# address
/0:Objects/2:Demo/2:Dynamic/2:Int32

Output

A JSON object representing the node's DataValue. This includes the value, status code, and server/source timestamps. For example:

JSON

{
  "value": {
    "dataType": "Int32",
    "value": 12345
  },
  "statusCode": {
    "name": "Good",
    "value": 0
  },
  "serverTimestamp": "2025-07-11T08:52:34.000Z",
  "sourceTimestamp": "2025-07-11T08:52:34.000Z"
}

readVariable

Reads the value of a single variable from the server. This is a convenience function that extracts just the value from the node's data.

Parameters

  • address: The address of the variable, which can be its nodeId (recommended) or a full browse path.

Example: Read using nodeId

# address
ns=2;s=Demo.Dynamic.Int32

Example: Read using Browse Path

# address
/0:Objects/2:Demo/2:Dynamic/2:Int32

Output

The raw value of the variable (e.g., a number, a string, a boolean, or an array).

writeVariable

Writes a new value to a variable on the server. The function automatically handles the conversion from a standard JavaScript type to the required OPC UA data type.

Parameters

  • address: The nodeId or browse path of the variable to write to.

  • value: The new value to set.

Example

# address
ns=2;s=Demo.Dynamic.Int32
# value
42

Output

The function returns null on a successful write or throws an error on failure.

callMethod

Invokes a method on an OPC UA object on the server. Input arguments are automatically converted to the correct data types as defined by the method on the server.

Parameters

  • methodAddress: The nodeId or browse path of the method to call.

  • inputValues: An array of values to pass as input arguments to the method.

Example

This example calls a method that takes two input arguments.

# methodAddress
ns=2;s=Demo.Methods.Multiply
# inputValues
[ 5, 10 ]

Output

An array containing the output arguments returned by the method call.

monitorNode

Subscribes to changes for an entire OPC UA node. The provided callback function is triggered with the full node data object (including value, status, and timestamps) whenever a change is detected by the server.

Parameters

  • address: The nodeId or browse path of the node to monitor.

  • listener: The callback function that will receive the full data object on change.

  • options: An object to configure the subscription.

    • samplingInterval: How often (in milliseconds) the server should check for changes. Default is 1000.

Example

# address
ns=2;s=Demo.Dynamic.UInt16
# listener
<callback>
# options
samplingInterval: 5000

Output

Returns a unique nodeId string that acts as an identifier for this monitored item, which is needed for stopMonitor.

monitorVariable

Subscribes to value changes for a specific variable. A callback function is triggered every time the server reports a new value.

Parameters

  • address: The nodeId or browse path of the variable to monitor.

  • listener: The callback function that will receive the new value.

  • options: An object to configure the subscription.

    • samplingInterval: How often (in milliseconds) the server should check the variable for changes. Default is 1000.

Example

# address
ns=2;s=Demo.Dynamic.UInt16
# listener
<callback>
# options
samplingInterval: 5000

Output

Returns a unique nodeId string that acts as an identifier for this monitored item. This ID is used to stop the monitoring later.

stopMonitor

Terminates an active subscription for a monitored item.

Parameters

  • nodeId: The identifier string that was returned by a previous call to monitorNode or monitorVariable.

Example

# nodeId
ns=2;s=Demo.Dynamic.UInt16

Output

Returns true if the subscription was terminated successfully.

browseDirectory

Recursively browses a file-system-like directory structure exposed by an OPC UA server.

Parameters

  • address: The nodeId or browse path of the starting directory node.

Output

A nested array of objects representing the directory structure.

readFile

Reads the entire content of a file exposed by the OPC UA server's file transfer feature.

Parameters

  • address: The nodeId or browse path of the file node on the server.

Example

# address
ns=2;s=Demo.Files.TextFile

Output

The complete content of the file, encoded as a base64 string.

writeFile

Creates a new file in a specified folder on the server and uploads content to it.

Parameters

  • folderAddress: The nodeId or browse path of the folder where the file will be created.

  • newFileName: The name for the new file.

  • pathOrBase64: The content to upload, either as a base64 string or a local file system path.

Example

# folderAddress
ns=2;s=Demo.Files
# newFileName
report.txt
# pathOrBase64
SGVsbG8sIFdvcmxkIQ==

Output

The nodeId of the newly created file on the server.

deleteFile

Deletes a file from a folder on the OPC UA server.

Parameters

  • folderAddress: The nodeId or browse path of the folder containing the file.

  • fileName: The name of the file to delete.

Example

# folderAddress
ns=2;s=Demo.Files
# fileName
report.txt

Output

Returns true if the file was deleted successfully.

listenToEvents

Registers a callback function to receive important lifecycle events from the client, such as Connected, Connection Lost, Session Closed, etc. This is useful for monitoring the health of the connection.

Parameters

  • listener: The callback function to receive event strings.

Output

Returns true.

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