Logger: JSON

The JsonExporter in TriFrost outputs logs as pure JSON — making it ideal for structured logging pipelines, file sinks, or log aggregation systems that expect newline-delimited JSON (NDJSON).

It supports:

JSON-formatted log output
Optional custom sink function
Field redaction (omit)

It's especially useful when:

You’re running in a container and want to stdout to a JSON collector
You want logs to be testable/assertable in memory
You’re building your own log ingestion flow

It's the default exporter in production for the Workerd runtime.

📥 Import and Use

import {App, JsonExporter} from '@trifrost/core';

new App({
  ...
  tracing: {
    exporters: ({env}) => [
      new JsonExporter({
        omit: [...], // see below
        sink: log => process.stdout.write(JSON.stringify(log) + '\n')
      }),
    ],
  }
  ...
})

You provide this when configuring your App setup, there's sensible defaults at play so in most cases new JsonExporter() will be enough.

Note: If no sink is provided, logs are written to console[log.level].

⚙️ Available Options

omit: TriFrostLogScramblerValue[]
Keys to redact from data/ctx/global payloads. Learn more here
default: OMIT_PRESETS.default
sink: (entry:JsonExporterEntry) => void
Custom log writer — lets you pipe logs to a file, socket, or in-memory store.

JsonExporterEntry

The JsonExporterEntry object looks like this:

{
  "time": "2025-06-06T10:30:00.000Z",
  "level": "info",
  "message": "User logged in",
  "trace_id": "3c51d...",
  "span_id": "a1b2c3d4",
  "ctx": {...},
  "data": {...},
  "global": {...}
}

This shape is structured and predictable, making it ideal for ingestion by:

Datadog
Vector.dev
FluentBit
Loki
CloudFlare observability (TriFrost is using this)
...

Examples

Sink

import {JsonExporter} from '@trifrost/core';
import {LogService} from './LogService'; /* eg: singleton instance which pushes to file */

new JsonExporter({
  sink: log => LogService.push(JSON.stringify(log)),
});

Override Defaults

new JsonExporter({
  omit: [{global: 'ssn'}] // Only redact 'ssn', not full default list
});

Note: ⚠️ Be very careful, you dont want to leak secrets, our advice is to always do something akin to omit: [...OMIT_PRESETS.default, (your own expansion)]

👉 See Scrambling Hygiene for full explanation

Best Practices

✅ Use in CI, production, or custom log sinks
✅ Pipe output to file or stream sinks (via sink)
✅ Keep one exporter per format — don’t double-format
💡 You can use this exporter in tandem with JsonExporter or OtelHttpExporter
💡 Want to go fancy? Make use of TriFrost's isDevMode function to refine between dev and prod

TriFrost Docs