v8.setFlagsFromString

History

v8.setFlagsFromString(flags): void

Attributes

flags:string

The v8.setFlagsFromString() method can be used to programmatically set V8 command-line flags. This method should be used with care. Changing settings after the VM has started may result in unpredictable behavior, including crashes and data loss; or it may simply do nothing.

The V8 options available for a version of Node.js may be determined by running node --v8-options.

Usage:

import { setFlagsFromString } from 'node:v8';
import { setInterval } from 'node:timers';

// setFlagsFromString to trace garbage collection events
setFlagsFromString('--trace-gc');

// Trigger GC events by using some memory
let arrays = [];
const interval = setInterval(() => {
  for (let i = 0; i < 500; i++) {
    arrays.push(new Array(10000).fill(Math.random()));
  }

  if (arrays.length > 5000) {
    arrays = arrays.slice(-1000);
  }

  console.log(`\n* Created ${arrays.length} arrays\n`);
}, 100);

// setFlagsFromString to stop tracing GC events after 1.5 seconds
setTimeout(() => {
  setFlagsFromString('--notrace-gc');
  console.log('\nStopped tracing!\n');
}, 1500);

// Stop triggering GC events altogether after 2.5 seconds
setTimeout(() => {
  clearInterval(interval);
}, 2500);

JavaScript

const { setFlagsFromString } = require('node:v8');
const { setInterval } = require('node:timers');

// setFlagsFromString to trace garbage collection events
setFlagsFromString('--trace-gc');

// Trigger GC events by using some memory
let arrays = [];
const interval = setInterval(() => {
  for (let i = 0; i < 500; i++) {
    arrays.push(new Array(10000).fill(Math.random()));
  }

  if (arrays.length > 5000) {
    arrays = arrays.slice(-1000);
  }

  console.log(`\n* Created ${arrays.length} arrays\n`);
}, 100);

// setFlagsFromString to stop tracing GC events after 1.5 seconds
setTimeout(() => {
  console.log('\nStopped tracing!\n');
  setFlagsFromString('--notrace-gc');
}, 1500);

// Stop triggering GC events altogether after 2.5 seconds
setTimeout(() => {
  clearInterval(interval);
}, 2500);

JavaScript