eventLoopLag.ts

export const eventLoopLag = (() => {
  let count = 0;
  let avg: number | null = null;
  let max: number | null = null;
  const avgMax = () => `Average: ${avg?.toFixed(1)} ms - Max: ${max?.toFixed(1)} ms`;

  const track = (countAverages = false, printAveragesEvery = 1_000_000, printImmediatelyThresholdMs = 10) => {
    const start = performance.now();
    setImmediate(() => {
      const delay = performance.now() - start;
      if (delay >= printImmediatelyThresholdMs) {
        console.log(`Event Loop LAG: ${delay.toFixed(1)} ms - previously -> ${avgMax()}`);
        count = 0;
        avg = null;
        max = null;
      } else if (countAverages) {
        count++;
        avg = avg ? (avg + delay) / 2 : delay;
        max = max ? Math.max(max, delay) : delay;
      }
      if (count >= printAveragesEvery) {
        console.log(`${count} counts. ${avgMax()}`);
        count = 0;
        avg = null;
        max = null;
      }
      track(countAverages, printAveragesEvery, printImmediatelyThresholdMs);
    });
  };
  return track;
})();
eventLoopLag(true);

printMemoryWhileCallingGC.ts

import * as process from 'process';
import { setFlagsFromString } from 'v8';
import { runInNewContext } from 'vm';

setInterval(() => {
  const memoryUsage = process.memoryUsage();
  console.table([{
    'RSS (Resident Set Size)': `${Math.round(memoryUsage.rss / 1024 / 1024)} MB`,
    'Heap Total': `${Math.round(memoryUsage.heapTotal / 1024 / 1024)} MB`,
    'Heap Used': `${Math.round(memoryUsage.heapUsed / 1024 / 1024)} MB`,
    'External': `${Math.round(memoryUsage.external / 1024 / 1024)} MB`,
    'Array Buffers': `${Math.round(memoryUsage.arrayBuffers / 1024 / 1024)} MB`,
  }]);
  
  
  // call gc
  setFlagsFromString('--expose_gc');
  const gc = runInNewContext('gc'); // nocommit
  gc();
}, 500).unref();