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Timing and Grouping ​

Problem ​

You need to measure how long a code block takes and group the related log entries so they are easy to correlate in output — without sprinkling Date.now() calls across the codebase.

Solution ​

Use time(label, fn) to measure execution and groupCollapsed(label, fn) to nest related log lines under a collapsible group in the console.

ts
import { createLogger } from '@vielzeug/rune';

const log = createLogger('checkout');
const order = { id: 'order-42' };

async function processOrder(value: typeof order): Promise<string> {
  return value.id;
}

const result = await log.groupCollapsed('Checkout', async () => {
  log.info('validating cart');

  return log.time('process order', () => processOrder(order));
});

console.log(result);

Pitfalls ​

  • time() always emits at debug level with the label as the log message and { duration_ms } in context. If logLevel is above debug, the timer still runs but no entry is emitted. Set logLevel: 'debug' when capturing timing data.
  • time() measures wall-clock time via performance.now(). For async functions, it covers total elapsed time including I/O wait — not CPU time. Long I/O waits will inflate the result.
  • group() and groupCollapsed() call console.group/console.groupEnd regardless of which transport is configured. They are visual wrappers for the console; other transports (remote, JSON, batch) receive entries as normal flat events with no grouping semantics.
  • When logLevel is 'off', the group wrapper is bypassed entirely but the callback still executes.