slowwatch

Only log something when it becomes slow.

One small problem. One obvious API. Very little setup. Immediate value.

console.time gives you raw numbers. Raw numbers don't tell you whether performance is getting worse. slowwatch watches every labelled execution, stays silent while things are fast, warns past a budget, and flags regressions against your own baseline.

Install

npm i slowwatch

Usage

import { slow } from "slowwatch";

const user = await slow("load-user", () => getUser());
// fast → prints nothing
// slow → 🐌 "load-user" took 842ms  (Expected < 200ms)

Thresholds

slow("load-user", getUser, { warn: 200, error: 1000 });
// 🐌  warning past 200ms
// 🚨  critical past 1s ("Critical threshold is 1s")

Automatic regression detection

After a few baseline runs, a clearly slower execution is flagged:

Performance regression

"load-user"

Previous average:  112ms
Current:          391ms

249% slower

Manual timer

import { start } from "slowwatch";

const timer = start("database-query");
await query();
timer.end(); // records + warns if slow

Decorator

import { monitorSlow } from "slowwatch";

const loadUser = monitorSlow("load-user", originalLoadUser, { warn: 200 });

Stats

import { stats } from "slowwatch";

stats("load-user");
// { count, avg, median, p95, min, max, latest }

Configure

import { configure, slow } from "slowwatch";

configure({
  output: "console",      // or "silent" | "buffer" | your own logger
  defaults: { warn: 500, error: 5000, baseline: true },
});

Zero dependencies. ESM + CJS + .d.ts. Node >= 18.

License

MIT