Javascript Code

Use Javascript code snippets to transform Streamfold events.

Intro

With the Javascript code function you can transform Streamfold events using familiar Javascript. This is useful when the built-in transform functions don't support an existing use case. For example, here's a small Javascript code sample that lower cases the service name.

const { fields } = getEvent();

fields.service = fields.service.toLowerCase()

Required Configuration

• Javascript snippet: A snippet of Javascript code to execute per event.

Examples

Retrieving fields and metadata

The getEvent() function returns the event fields and the event metadata. The fields represent the top-level fields of the event and meta represents the metadata of the event.

const { fields, meta } = getEvent();

if (meta.source.type === "datadog_agent" && meta.type === "metrics") {
    fields['_num_metrics'] = fields.series.length;
}

if (meta.source.type === "datadog_agent" && meta.type === "sketches") {
    fields['_num_metrics'] = fields.sketches.length;
}

Dropping or replacing event fields

Any returned value from the code snippet will replace the fields structure of the event. Returning null will drop the event entirely.

Return a new event with only the top-level fields service and host.

const { fields: f } = getEvent();

return {
    service: f.serviceName,
    host: f.hostname,
}

A return without a value (undefined) will default to the existing fields.

const { fields: f, meta: m } = getEvent();

// Keep logs
if (m.type === "logs") {
    return
}

// Drop all but metrics
if (m.type !== "metrics") {
    return null
}

// Keep only metrics from production
f.series = f.series.filter((s) => s.tags.includes("env:production"))

Event time

The event time is included in the events as the field _time. It is encoded in RFC3339Nano format as a string.

const { fields: f } = getEvent();

const d = new Date(f['_time']);
f.month = d.getMonth()

Custom functions

Custom functions can be defined and used in code snippets as well.

function resStrAttr(res, key) {
    const a = res.attributes.find((a) => a.key === key);
    
    return a.value?.stringValue;
}

const { fields: f } = getEvent();

// strip logs of currencyservice
f.resourceLogs = f.resourceLogs.filter((r) => resStrAttr(r.resource, "service.name") !== "currencyservice");

if (f.resourceLogs.length === 0) {
    return null
}

Notes

The Javascript code function is compatible with ECMAScript 5.1.

The Javascript code function is a powerful way to extend the capabilities of Streamfold beyond what built-in functions can provide; however, it comes at the cost of introducing overhead in stream processing. Therefore, it is still better to use built-in functions when possible. Over time the set of built-in functions will expand to cover more use cases. Additionally, the performance of Javascript code execution will be improved.