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Quick start

This page is one complete script. Copy it into quick-start.ts, run it with node --experimental-strip-types quick-start.ts (Node 24 runs TypeScript directly), and you will see structured JSON on stdout.

quick-start.ts
import { createLogger } from '@tevm/logger'
 
// One logger per component. `name` shows up on every record it emits.
const logger = createLogger({
	name: 'quick-start',
	level: 'debug',
})
 
// A message on its own.
logger.info('starting up')
 
// A message with structured fields. The object goes FIRST, the message second.
logger.info({ chainId: 1, port: 8545 }, 'listening for JSON-RPC requests')
 
// Levels below the configured `level` are dropped with almost no cost.
logger.debug({ cacheSize: 128 }, 'warmed the state cache')
logger.trace('you will not see this — level is debug')
 
// Errors: pass the Error under the `err` key so pino serializes the stack.
try {
	throw new Error('reverted: out of gas')
} catch (error) {
	logger.error({ err: error }, 'call failed')
}
 
logger.warn({ blockNumber: 21_000_000n }, 'fork block is stale')

The output

Each call writes one newline-delimited JSON object to stdout:

{"level":30,"time":1739577600000,"pid":41234,"hostname":"nuc","name":"quick-start","msg":"starting up"}
{"level":30,"time":1739577600001,"pid":41234,"hostname":"nuc","name":"quick-start","chainId":1,"port":8545,"msg":"listening for JSON-RPC requests"}
{"level":20,"time":1739577600001,"pid":41234,"hostname":"nuc","name":"quick-start","cacheSize":128,"msg":"warmed the state cache"}
{"level":50,"time":1739577600002,"pid":41234,"hostname":"nuc","name":"quick-start","err":{"type":"Error","message":"reverted: out of gas","stack":"Error: reverted: out of gas\n    at ..."},"msg":"call failed"}
{"level":40,"time":1739577600002,"pid":41234,"hostname":"nuc","name":"quick-start","blockNumber":"21000000","msg":"fork block is stale"}

Three things to notice:

  1. level is a number, not a string (info is 30, warn 40, error 50). That is pino's wire format; log viewers and pino-pretty map it back to a name.
  2. name is the value you passed to createLogger, on every record. That is the field you filter on to see just one Tevm subsystem.
  3. blockNumber was a bigint and came out as a string. pino stringifies BigInts rather than throwing, which matters constantly in Ethereum code.

Making it readable while you develop

Raw JSON is for machines. While developing, pipe it through pino-pretty:

pnpm add -D pino-pretty
node --experimental-strip-types quick-start.ts | npx pino-pretty

See Pretty printing in development for how to wire it in-process instead of piping.

Where to go next

Edit on GitHub