Heartbeat.js - find event loop blocking code by looking for blown timeouts

heartbeat.js

// Heartbeat log script for node.js. Use this to sniff out code that blocks
// your event loop; heartbeats will take longer if the event loop is
// blocked.
// Just require('./heartbeat.js'); ==OR== require('./heartbeat.js')(3000);
module.exports = go;

var DEFAULT_HEARTBEAT_MS = 2000;
var startedAt, loop;

go();

function go(newInterval) {
	newInterval = newInterval || DEFAULT_HEARTBEAT_MS;
	clearInterval(loop);
	startedAt = Date.now();
	loop = setInterval(beat, newInterval);
}

function beat() {
	var elapsed = Date.now() - startedAt;
	console.warn('heartbeat %d: %s', process.pid, elapsed);
	startedAt = Date.now();
}