packages/react-server/core/logging/stats.js
function wrapLogger(getLoggerForConfig, opts) {

	var mainLogger    = getLoggerForConfig('main',  opts)
		,   timeLogger    = getLoggerForConfig('time',  opts)
		,   gaugeLogger   = getLoggerForConfig('gauge', opts)
		,   classifyTime  = makeTimeClassifier(opts)
		,   classifyGauge = makeGaugeClassifier(opts)

	// These are methods that are exposed on the primary logger.
	// They just dispatch to appropriate log levels on secondary loggers.
	mainLogger.time  = (token, ms,  opts) => timeLogger [classifyTime (ms,  opts)](token, {ms });
	mainLogger.gauge = (token, val, opts) => gaugeLogger[classifyGauge(val, opts)](token, {val});

	// Expose these.
	mainLogger.timeLogger  = timeLogger;
	mainLogger.gaugeLogger = gaugeLogger;

	// This is just a convenience wrapper around the `time` method.
	mainLogger.timer = (token, opts) => {

		var t0 = new Date // For use by `timer.stop`.
			,   tt = t0       // For use by `timer.tick`.
			,   nt = 0        // Number of times `tick` has been called.
			,   ct = 0        // For storing return values.

		return {

			// The `stop` method logs the total elapsed time since
			// timer creation.
			stop: () => (mainLogger.time(token, ct = new Date - t0, opts), ct),

			// The `tick` method logs the time elapsed since the
			// last call to `tick` (or since timer creation).  A
			// tick may be named.  If a name is not passed in the
			// number of times `tick` has been called on this
			// timer will be used.  Don't mix named and un-named
			// ticks.
			tick: (name) => {
				var now = new Date

				name || (name = `tick_${nt++}`);

				mainLogger.time(`${token}.${name}`, ct=now-tt, opts);

				tt = now;

				return ct
			},
		};
	}

	return mainLogger;
}
function wrapLogger(getLoggerForConfig, opts) {

	var mainLogger    = getLoggerForConfig('main',  opts)
		,   timeLogger    = getLoggerForConfig('time',  opts)
		,   gaugeLogger   = getLoggerForConfig('gauge', opts)
		,   classifyTime  = makeTimeClassifier(opts)
		,   classifyGauge = makeGaugeClassifier(opts)

	// These are methods that are exposed on the primary logger.
	// They just dispatch to appropriate log levels on secondary loggers.
	mainLogger.time  = (token, ms,  opts) => timeLogger [classifyTime (ms,  opts)](token, {ms });
	mainLogger.gauge = (token, val, opts) => gaugeLogger[classifyGauge(val, opts)](token, {val});

	// Expose these.
	mainLogger.timeLogger  = timeLogger;
	mainLogger.gaugeLogger = gaugeLogger;

	// This is just a convenience wrapper around the `time` method.
	mainLogger.timer = (token, opts) => {

		var t0 = new Date // For use by `timer.stop`.
			,   tt = t0       // For use by `timer.tick`.
			,   nt = 0        // Number of times `tick` has been called.
			,   ct = 0        // For storing return values.

		return {

			// The `stop` method logs the total elapsed time since
			// timer creation.
			stop: () => (mainLogger.time(token, ct = new Date - t0, opts), ct),

			// The `tick` method logs the time elapsed since the
			// last call to `tick` (or since timer creation).  A
			// tick may be named.  If a name is not passed in the
			// number of times `tick` has been called on this
			// timer will be used.  Don't mix named and un-named
			// ticks.
			tick: (name) => {
				var now = new Date

				name || (name = `tick_${nt++}`);

				mainLogger.time(`${token}.${name}`, ct=now-tt, opts);

				tt = now;

				return ct
			},
		};
	}

	return mainLogger;
}
Each logger actually has some secondary loggers attached to it for stats. This helper wires them up.