JavaScript Eval

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Description

The JavaScript Eval processor allows you to write custom JavaScript functions to transform and enrich events. It:

• Executes user-defined JavaScript code
• Provides full access to input event data
• Supports complex data transformations
• Enables dynamic field creation and modification

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Required Input

The processor works with any input event stream. All fields from the input event are available as properties in the JavaScript function.

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Configuration

JavaScript Function

You need to provide a JavaScript function that processes the input event and returns a new event object. The function must:

• Be named process
• Accept a single parameter containing the input event
• Return a map/object with the output fields

Example function structure:

    function process(event) {
        // do processing here.
        // return a map with fields that matched defined output schema.
        return {id: event.id, tempInCelsius: (event.tempInKelvin - 273.15)};
    }

The defined output schema must match the event that is returned by the JavaScript function.

Output

The processor forwards a new event containing the fields returned by your JavaScript function.

Example

Input Event

{
  "temperature": 25.5,
  "humidity": 60,
  "timestamp": 1586380105115
}

Configuration

function process(event) {
    // Convert temperature from Celsius to Fahrenheit
    const tempF = (event.temperature * 9/5) + 32;
    
    // Calculate heat index
    const heatIndex = calculateHeatIndex(tempF, event.humidity);
    
    // Return new event with transformed data
    return {
        temperature_celsius: event.temperature,
        temperature_fahrenheit: tempF,
        humidity: event.humidity,
        heat_index: heatIndex,
        timestamp: event.timestamp
    };
}

function calculateHeatIndex(temp, humidity) {
    // Simplified heat index calculation
    return temp + (humidity * 0.1);
}

Output Event

{
  "temperature_celsius": 25.5,
  "temperature_fahrenheit": 77.9,
  "humidity": 60,
  "heat_index": 83.9,
  "timestamp": 1586380105115
}

Use Cases

1. Data Transformation

   • Unit conversions
   • Data normalization
   • Complex calculations
   • Field restructuring

2. Data Enrichment

   • Adding derived fields
   • Computing statistics
   • Combining multiple fields
   • Creating calculated metrics

3. Custom Logic

   • Business rules implementation
   • Conditional transformations
   • Data validation
   • Custom algorithms

Notes

• The JavaScript function runs in a GraalVM JavaScript environment
• All input fields are accessible as properties of the event object
• The function must return a valid JavaScript object
• Error handling should be implemented in the JavaScript code
• Complex JavaScript operations are supported
• The function is executed for each incoming event, but state can be kept