log component: Log component. Used to format message content and record it to logs, supports customizing log format using JavaScript scripts.

JavaScript scripts support ECMAScript 5.1(+) syntax specifications and some ES6 specifications, such as: async/await/Promise/let. Custom Go functions can be called within scripts, please refer to udf.

Configuration

Field	Type	Description	Default Value
jsScript	string	Log formatting script	None

• jsScript: The JavaScript script used to format log content. This field serves as the body of the following function:

      function ToString(msg, metadata, msgType, dataType) { 
          ${jsScript} 
       }
  

  Function parameter descriptions:

  • msg: Message content, intelligently converted based on data type
    • When dataType=JSON, type is jsonObject, fields can be accessed using msg.field
    • When dataType=BINARY, type is Uint8Array, byte-level operations are possible
    • For other dataTypes, type is string
  • metadata: Message metadata, type is jsonObject
  • msgType: Message type, type is string
  • dataType: Message data type, type is string (e.g., JSON, TEXT, BINARY, etc.)

  The function return value must be of type string, and the returned string will be recorded as the log content.

TIP

• The logger can be configured via config.Logger
• Default output is to the console
• Supports configuring log level, output format, etc.
• Supports intelligent processing of multiple data types, including JSON object access and binary data handling

Data Type Support

This component supports multiple message data types:

• JSON type: Automatically parsed into a JavaScript object, properties can be accessed directly
• BINARY type: Converted to Uint8Array, convenient for byte-level operations
• TEXT type: Remains in string format
• Other types: Uniformly processed as strings

Relation Type

• Success: Execution successful, message is sent to the Success chain
• Failure: Execution failed, message is sent to the Failure chain

Execution Result

This component does not modify the content of msg.Data and msg.Metadata.

Configuration Examples

Basic Example

  {
    "id": "s1",
    "type": "log",
    "name": "Log Message",
    "configuration": {
      "jsScript": "return 'Incoming message:\\n' + JSON.stringify(msg) + '\\nIncoming metadata:\\n' + JSON.stringify(metadata);"
    }
  }

JSON Data Processing Example

  {
    "id": "s2",
    "type": "log",
    "name": "Log Temperature",
    "configuration": {
      "jsScript": "if (dataType === 'JSON' && msg.temperature !== undefined) { return 'Temperature: ' + msg.temperature + '°C, Device: ' + (metadata.deviceId || 'unknown'); } else { return 'Non-JSON message: ' + JSON.stringify(msg); }"
    }
  }

Binary Data Processing Example

  {
    "id": "s3",
    "type": "log",
    "name": "Log Binary Data",
    "configuration": {
      "jsScript": "if (dataType === 'BINARY') { return 'Binary data length: ' + msg.length + ' bytes, first byte: ' + (msg.length > 0 ? msg[0] : 'empty'); } else { return 'Text message: ' + msg; }"
    }
  }

Intelligent Multi-Type Processing Example

  {
    "id": "s4",
    "type": "log",
    "name": "Intelligent Log Formatting",
    "configuration": {
      "jsScript": "var prefix = '[' + msgType + '][' + dataType + '] '; switch(dataType) { case 'JSON': return prefix + 'JSON data: ' + JSON.stringify(msg); case 'BINARY': return prefix + 'Binary data: ' + msg.length + ' bytes'; default: return prefix + 'Text data: ' + msg; }"
    }
  }