effect-io-ai

Package: effect
Module: Logger

Logger.formatJson

A Logger which outputs logs using a structured format serialized as JSON on a single line.

Details

For example, a JSON entry can render as {"message":["hello"],"level":"INFO", "timestamp":"2025-01-03T14:28:57.508Z","annotations":{"key":"value"}, "spans":{"label":0},"fiberId":"#1"}.

Example (Formatting logs as JSON)

import { Effect, Logger } from "effect"

// Use the JSON format logger
const jsonLoggerProgram = Effect.log("Hello JSON Format").pipe(
  Effect.provide(Logger.layer([Logger.formatJson]))
)

// Perfect for log aggregation and processing systems
const productionProgram = Effect.gen(function*() {
  yield* Effect.log("Server started", { port: 3000, env: "production" })
  yield* Effect.logInfo("Request received", {
    method: "GET",
    path: "/api/users"
  })
  yield* Effect.logError("Database error", { error: "Connection timeout" })
}).pipe(
  Effect.annotateLogs("service", "api-server"),
  Effect.withLogSpan("request-processing"),
  Effect.provide(Logger.layer([Logger.formatJson]))
)

// Adapt the JSON string before giving it to an output sink
const envelopedJsonLogger = Logger.map(
  Logger.formatJson,
  (jsonString) => `{"service":"api-server","entry":${jsonString}}`
)

const envelopedConsoleLogger = Logger.withConsoleLog(envelopedJsonLogger)

Signature

declare const formatJson: Logger<unknown, string>

Source

Since v4.0.0