Node.js

Overview

Node.js is ideal for asynchronous operations, JSON processing, and web-related code. Runner Codes provides Node.js 22 LTS with full ES modules support.

Specifications

Property	Value
Docker Image	node:22-alpine
Version	Node.js v22.21.1
Rootfs Size	250 MB
Execution	Interpreted (V8 JIT)
File Extension	.js
Run Command	node {file}
Execution Time	~2.7s

warning

Kernel 5.10+ Required: Node.js requires Linux kernel 5.10 or newer to work correctly in Firecracker microVMs. Older kernels (4.14) cause Node.js to hang due to libuv/epoll compatibility issues.

Run sudo infra.operator setup to download the correct kernel version.

1. Create Rootfs from Docker

sudo infra.operator rootfs from-docker --name nodejs --image node:22-alpine --size 250

2. Create Snapshot

sudo infra.operator snapshot create --lang nodejs --mem 512 --vcpus 1

3. Upload rootfs to S3

sudo infra.operator rootfs upload --lang nodejs --bucket runner-codes

3. Upload snapshot to S3

sudo infra.operator snapshot upload --lang nodejs --bucket runner-codes

4. Test Execution

sudo infra.operator host --lang nodejs --code "console.log(process.version)" --mem 512 --vcpus 1 --snapshot

Execution Flow

Examples

Hello World

Request

{
  "language": "node",
  "files": [
    {
      "name": "main.js",
      "content": "console.log('Hello from Node.js!')"
    }
  ]
}

Response

{
  "status": "success",
  "stdout": "Hello from Node.js!\n",
  "stderr": null,
  "exception": null,
  "executionTime": 45
}

With STDIN Input

Request

{
  "language": "node",
  "stdin": "Alice",
  "files": [
    {
      "name": "main.js",
      "content": "const readline = require('readline');\nconst rl = readline.createInterface({ input: process.stdin });\nrl.on('line', (name) => {\n  console.log(`Hello, ${name}!`);\n  rl.close();\n});"
    }
  ]
}

Response

{
  "status": "success",
  "stdout": "Hello, Alice!\n",
  "stderr": null,
  "exception": null,
  "executionTime": 52
}

Variables and Template Literals

Request

{
  "language": "node",
  "files": [
    {
      "name": "main.js",
      "content": "const name = 'Alice';\nconst age = 30;\nconsole.log(`Hello, ${name}! You are ${age} years old.`);"
    }
  ]
}

Response

{
  "status": "success",
  "stdout": "Hello, Alice! You are 30 years old.\n",
  "stderr": null,
  "exception": null,
  "executionTime": 40
}

Arrow Functions

Request

{
  "trace_id": "node-arrow-001",
  "lang": "node",
  "code": "const numbers = [1, 2, 3, 4, 5];\nconst doubled = numbers.map(n => n * 2);\nconst sum = numbers.reduce((a, b) => a + b, 0);\nconsole.log('Doubled:', doubled);\nconsole.log('Sum:', sum);",
  "timeout": 10
}

Response

{
  "trace_id": "node-arrow-001",
  "stdout": "Doubled: [ 2, 4, 6, 8, 10 ]\nSum: 15\n",
  "stderr": "",
  "exit_code": 0
}

Async/Await

Request

{
  "trace_id": "node-async-001",
  "lang": "node",
  "code": "async function delay(ms) {\n  return new Promise(resolve => setTimeout(resolve, ms));\n}\n\nasync function main() {\n  console.log('Start');\n  await delay(100);\n  console.log('After 100ms');\n  await delay(100);\n  console.log('Done');\n}\n\nmain();",
  "timeout": 10
}

Response

{
  "trace_id": "node-async-001",
  "stdout": "Start\nAfter 100ms\nDone\n",
  "stderr": "",
  "exit_code": 0
}

Promises

Request

{
  "trace_id": "node-promise-001",
  "lang": "node",
  "code": "const promise1 = Promise.resolve(10);\nconst promise2 = Promise.resolve(20);\nconst promise3 = Promise.resolve(30);\n\nPromise.all([promise1, promise2, promise3])\n  .then(values => {\n    console.log('Values:', values);\n    console.log('Total:', values.reduce((a, b) => a + b, 0));\n  });",
  "timeout": 10
}

Response

{
  "trace_id": "node-promise-001",
  "stdout": "Values: [ 10, 20, 30 ]\nTotal: 60\n",
  "stderr": "",
  "exit_code": 0
}

Object Destructuring

Request

{
  "trace_id": "node-destruct-001",
  "lang": "node",
  "code": "const user = { name: 'Bob', age: 25, city: 'LA' };\nconst { name, ...rest } = user;\nconsole.log('Name:', name);\nconsole.log('Rest:', rest);",
  "timeout": 10
}

Response

{
  "trace_id": "node-destruct-001",
  "stdout": "Name: Bob\nRest: { age: 25, city: 'LA' }\n",
  "stderr": "",
  "exit_code": 0
}

Classes

Request

{
  "trace_id": "node-class-001",
  "lang": "node",
  "code": "class Animal {\n  constructor(name) {\n    this.name = name;\n  }\n  speak() {\n    console.log(`${this.name} makes a sound`);\n  }\n}\n\nclass Dog extends Animal {\n  speak() {\n    console.log(`${this.name} barks`);\n  }\n}\n\nconst dog = new Dog('Rex');\ndog.speak();",
  "timeout": 10
}

Response

{
  "trace_id": "node-class-001",
  "stdout": "Rex barks\n",
  "stderr": "",
  "exit_code": 0
}

JSON Processing

Request

{
  "trace_id": "node-json-001",
  "lang": "node",
  "code": "const data = {\n  users: [\n    { id: 1, name: 'Alice' },\n    { id: 2, name: 'Bob' }\n  ]\n};\n\nconst json = JSON.stringify(data, null, 2);\nconsole.log('JSON:');\nconsole.log(json);\n\nconst parsed = JSON.parse(json);\nconsole.log('\\nUsers:', parsed.users.map(u => u.name).join(', '));",
  "timeout": 10
}

Response

{
  "trace_id": "node-json-001",
  "stdout": "JSON:\n{\n  \"users\": [\n    {\n      \"id\": 1,\n      \"name\": \"Alice\"\n    },\n    {\n      \"id\": 2,\n      \"name\": \"Bob\"\n    }\n  ]\n}\n\nUsers: Alice, Bob\n",
  "stderr": "",
  "exit_code": 0
}

Array Methods

Request

{
  "trace_id": "node-array-001",
  "lang": "node",
  "code": "const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];\n\nconst evens = numbers.filter(n => n % 2 === 0);\nconst squared = evens.map(n => n * n);\nconst sum = squared.reduce((a, b) => a + b, 0);\n\nconsole.log('Original:', numbers);\nconsole.log('Evens:', evens);\nconsole.log('Squared:', squared);\nconsole.log('Sum:', sum);",
  "timeout": 10
}

Response

{
  "trace_id": "node-array-001",
  "stdout": "Original: [\n  1, 2, 3, 4,  5,\n  6, 7, 8, 9, 10\n]\nEvens: [ 2, 4, 6, 8, 10 ]\nSquared: [ 4, 16, 36, 64, 100 ]\nSum: 220\n",
  "stderr": "",
  "exit_code": 0
}

Map and Set

Request

{
  "trace_id": "node-mapset-001",
  "lang": "node",
  "code": "// Map example\nconst map = new Map();\nmap.set('a', 1);\nmap.set('b', 2);\nmap.set('c', 3);\nconsole.log('Map size:', map.size);\nconsole.log('Map entries:', [...map.entries()]);\n\n// Set example\nconst set = new Set([1, 2, 2, 3, 3, 3]);\nconsole.log('Set values:', [...set]);",
  "timeout": 10
}

Response

{
  "trace_id": "node-mapset-001",
  "stdout": "Map size: 3\nMap entries: [ [ 'a', 1 ], [ 'b', 2 ], [ 'c', 3 ] ]\nSet values: [ 1, 2, 3 ]\n",
  "stderr": "",
  "exit_code": 0
}

Regular Expressions

Request

{
  "trace_id": "node-regex-001",
  "lang": "node",
  "code": "const text = 'Contact: [email protected] or [email protected]';\nconst emailRegex = /[\\w.-]+@[\\w.-]+\\.[a-z]{2,}/gi;\nconst emails = text.match(emailRegex);\nconsole.log('Found emails:', emails);",
  "timeout": 10
}

Response

{
  "trace_id": "node-regex-001",
  "stdout": "Found emails: [ '[email protected]', '[email protected]' ]\n",
  "stderr": "",
  "exit_code": 0
}

File Operations

Request

{
  "trace_id": "node-file-001",
  "lang": "node",
  "code": "const fs = require('fs');\n\n// Write file\nfs.writeFileSync('/tmp/test.txt', 'Hello, Node.js!\\nLine 2');\n\n// Read file\nconst content = fs.readFileSync('/tmp/test.txt', 'utf8');\nconsole.log('Content:');\nconsole.log(content);",
  "timeout": 10
}

Response

{
  "trace_id": "node-file-001",
  "stdout": "Content:\nHello, Node.js!\nLine 2\n",
  "stderr": "",
  "exit_code": 0
}

Complex Test: Comprehensive Node.js

Request

{
  "trace_id": "node-complex-001",
  "lang": "node",
  "code": "console.log('=== Node.js Complex Test ===');\nconsole.log();\n\n// Test 1: Fibonacci with memoization\nconsole.log('1. Fibonacci with memoization:');\nconst memo = {};\nfunction fib(n) {\n  if (n in memo) return memo[n];\n  if (n <= 1) return n;\n  memo[n] = fib(n - 1) + fib(n - 2);\n  return memo[n];\n}\nconst fibs = Array.from({length: 15}, (_, i) => fib(i));\nconsole.log(`   First 15: [${fibs.join(', ')}]`);\nconsole.log(`   Fib(50) = ${fib(50)}`);\n\n// Test 2: QuickSort\nconsole.log();\nconsole.log('2. QuickSort:');\nfunction quicksort(arr) {\n  if (arr.length <= 1) return arr;\n  const pivot = arr[Math.floor(arr.length / 2)];\n  const left = arr.filter(x => x < pivot);\n  const middle = arr.filter(x => x === pivot);\n  const right = arr.filter(x => x > pivot);\n  return [...quicksort(left), ...middle, ...quicksort(right)];\n}\nconst unsorted = [64, 34, 25, 12, 22, 11, 90];\nconsole.log(`   Input:  [${unsorted.join(', ')}]`);\nconsole.log(`   Output: [${quicksort(unsorted).join(', ')}]`);\n\n// Test 3: Object operations\nconsole.log();\nconsole.log('3. Object operations:');\nconst people = [\n  { name: 'Alice', age: 30, city: 'NYC' },\n  { name: 'Bob', age: 25, city: 'LA' },\n  { name: 'Charlie', age: 35, city: 'Chicago' }\n];\nconst byCity = Object.fromEntries(people.map(p => [p.city, p.name]));\nconsole.log(`   People: [${people.map(p => p.name).join(', ')}]`);\nconsole.log(`   By city: ${JSON.stringify(byCity)}`);\nconsole.log(`   Avg age: ${people.reduce((s, p) => s + p.age, 0) / people.length}`);\n\n// Test 4: Array methods\nconsole.log();\nconsole.log('4. Array methods:');\nconst numbers = Array.from({length: 10}, (_, i) => i + 1);\nconst squares = numbers.map(x => x * x);\nconst evens = numbers.filter(x => x % 2 === 0);\nconst sum = squares.reduce((a, b) => a + b, 0);\nconsole.log(`   Numbers: [${numbers.join(', ')}]`);\nconsole.log(`   Squares: [${squares.join(', ')}]`);\nconsole.log(`   Evens: [${evens.join(', ')}]`);\nconsole.log(`   Sum of squares: ${sum}`);\n\n// Test 5: Classes and inheritance\nconsole.log();\nconsole.log('5. Classes and inheritance:');\nclass Animal {\n  constructor(name) { this.name = name; }\n  speak() { return 'Some sound'; }\n}\nclass Dog extends Animal {\n  speak() { return `${this.name} says Woof!`; }\n}\nclass Cat extends Animal {\n  speak() { return `${this.name} says Meow!`; }\n}\nconst animals = [new Dog('Rex'), new Cat('Whiskers'), new Dog('Buddy')];\nanimals.forEach(a => console.log(`   ${a.speak()}`));\n\n// Test 6: Promises and async simulation\nconsole.log();\nconsole.log('6. Promise handling:');\nconst asyncOp = (val, delay) => new Promise(r => setTimeout(() => r(val * 2), delay));\nPromise.all([asyncOp(5, 10), asyncOp(10, 10), asyncOp(15, 10)])\n  .then(results => {\n    console.log(`   Results: [${results.join(', ')}]`);\n    console.log(`   Sum: ${results.reduce((a, b) => a + b, 0)}`);\n    \n    // Test 7: Destructuring and spread\n    console.log();\n    console.log('7. Destructuring and spread:');\n    const { name, ...rest } = people[0];\n    console.log(`   Name: ${name}`);\n    console.log(`   Rest: ${JSON.stringify(rest)}`);\n    const merged = [...numbers.slice(0, 3), ...numbers.slice(-3)];\n    console.log(`   Merged: [${merged.join(', ')}]`);\n    \n    // Test 8: String operations\n    console.log();\n    console.log('8. String operations:');\n    const text = 'Hello, World! Welcome to Node.js.';\n    console.log(`   Original: ${text}`);\n    console.log(`   Upper: ${text.toUpperCase()}`);\n    console.log(`   Words: ${text.split(' ').length}`);\n    console.log(`   Includes 'Node': ${text.includes('Node')}`);\n    \n    console.log();\n    console.log('=== All tests passed ===');\n  });",
  "timeout": 30
}

Response

{
  "trace_id": "node-complex-001",
  "stdout": "=== Node.js Complex Test ===\n\n1. Fibonacci with memoization:\n   First 15: [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377]\n   Fib(50) = 12586269025\n\n2. QuickSort:\n   Input:  [64, 34, 25, 12, 22, 11, 90]\n   Output: [11, 12, 22, 25, 34, 64, 90]\n\n3. Object operations:\n   People: [Alice, Bob, Charlie]\n   By city: {\"NYC\":\"Alice\",\"LA\":\"Bob\",\"Chicago\":\"Charlie\"}\n   Avg age: 30\n\n4. Array methods:\n   Numbers: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]\n   Squares: [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]\n   Evens: [2, 4, 6, 8, 10]\n   Sum of squares: 385\n\n5. Classes and inheritance:\n   Rex says Woof!\n   Whiskers says Meow!\n   Buddy says Woof!\n\n6. Promise handling:\n   Results: [10, 20, 30]\n   Sum: 60\n\n7. Destructuring and spread:\n   Name: Alice\n   Rest: {\"age\":30,\"city\":\"NYC\"}\n   Merged: [1, 2, 3, 8, 9, 10]\n\n8. String operations:\n   Original: Hello, World! Welcome to Node.js.\n   Upper: HELLO, WORLD! WELCOME TO NODE.JS.\n   Words: 5\n   Includes 'Node': true\n\n=== All tests passed ===\n",
  "stderr": "",
  "exit_code": 0
}

Available Built-in Modules

Module	Description
fs	File system operations
path	Path manipulation
os	OS information
util	Utility functions
crypto	Cryptographic functions
buffer	Binary data handling
stream	Streaming operations
events	Event emitter
url	URL parsing
querystring	Query string parsing
assert	Assertions

note

Network modules (http, https, net, etc.) are available but won't work since the VM has no network access.

Error Examples

Syntax Error

Request

{
  "trace_id": "node-err-syntax",
  "lang": "node",
  "code": "const x = {;",
  "timeout": 10
}

Response

{
  "trace_id": "node-err-syntax",
  "stdout": "",
  "stderr": "/tmp/job-node-err-syntax/script.js:1\nconst x = {;\n           ^\n\nSyntaxError: Unexpected token ';'\n    at ...\n",
  "exit_code": 1
}

Runtime Error

Request

{
  "trace_id": "node-err-runtime",
  "lang": "node",
  "code": "const obj = null;\nconsole.log(obj.property);",
  "timeout": 10
}

Response

{
  "trace_id": "node-err-runtime",
  "stdout": "",
  "stderr": "TypeError: Cannot read properties of null (reading 'property')\n    at Object.<anonymous> (/tmp/job-node-err-runtime/script.js:2:17)\n    at ...\n",
  "exit_code": 1
}

Module Not Found

Request

{
  "trace_id": "node-err-module",
  "lang": "node",
  "code": "const axios = require('axios');\nconsole.log(axios);",
  "timeout": 10
}

Response

{
  "trace_id": "node-err-module",
  "stdout": "",
  "stderr": "Error: Cannot find module 'axios'\n    at ...\n",
  "exit_code": 1
}

Performance

Operation	Time
Hello World	~100ms
Fibonacci(30)	~100ms (V8 JIT)
JSON parse/stringify (1KB)	~1ms
Array operations (10k items)	~5ms

Limitations

warning

The Node.js environment has the following limitations:

1. Kernel 5.10+ required: Older kernels cause Node.js to hang (libuv/epoll issues)
2. No npm install: External packages must be pre-installed in rootfs
3. No network: HTTP requests will fail
4. Memory limit: 512 MiB default
5. Timeout: Configurable, default 10 seconds
6. No persistence: Files are lost after execution
7. CommonJS only: ES modules require file extension changes

Adding npm Packages to Rootfs

Option 1: Custom Dockerfile (Recommended)

Create a custom Dockerfile with your packages:

Create custom Docker image with npm packages

FROM node:18-alpine
RUN npm install -g lodash moment uuid typescript

Build Docker image and create rootfs from it

docker build -t my-nodejs .
infra.operator rootfs from-docker --name nodejs --image my-nodejs --size 500

Create snapshot and upload to S3

infra.operator snapshot create --lang nodejs --mem 512 --vcpus 1
infra.operator rootfs upload --lang nodejs --bucket runner-codes
infra.operator snapshot upload --lang nodejs --bucket runner-codes

Option 2: Mount and modify existing rootfs

Mount the rootfs for editing

sudo mount -o loop /srv/firecracker/images/rootfs-nodejs.ext4 /mnt/rootfs

Prepare chroot environment

sudo cp /etc/resolv.conf /mnt/rootfs/etc/
sudo mount --bind /dev /mnt/rootfs/dev
sudo mount --bind /proc /mnt/rootfs/proc
sudo mount --bind /sys /mnt/rootfs/sys

Install packages and cleanup

sudo chroot /mnt/rootfs /bin/sh
npm install -g lodash moment uuid
exit
sudo umount /mnt/rootfs/sys
sudo umount /mnt/rootfs/proc
sudo umount /mnt/rootfs/dev
sudo umount /mnt/rootfs

Recreate snapshot and upload to S3

infra.operator snapshot create --lang nodejs --mem 512 --vcpus 1
infra.operator rootfs upload --lang nodejs --bucket runner-codes
infra.operator snapshot upload --lang nodejs --bucket runner-codes

Troubleshooting

Node.js hangs or times out with "signal: killed"

Problem: Node.js execution hangs and eventually times out with signal: killed error.

Cause: Linux kernel 4.14 has compatibility issues with Node.js libuv event loop in Firecracker microVMs.

Solution: Upgrade to kernel 5.10+

Run setup to download kernel 5.10

sudo infra.operator setup

Verify kernel path

ls -la /srv/firecracker/vmlinux

Recreate snapshots with new kernel

infra.operator snapshot create --lang nodejs --mem 512 --vcpus 1

EXT4 filesystem corruption after snapshot restore

Problem: Corrupt inode bitmap or similar errors after restoring snapshot.

Cause: Filesystem not synced before snapshot creation.

Solution: The snapshot creation now automatically syncs the filesystem. If issues persist:

Increase rootfs size

infra.operator rootfs from-docker --name nodejs --image node:18-alpine --size 500

Recreate snapshot

infra.operator snapshot create --lang nodejs --mem 512 --vcpus 1

Best Practices

Best Practices

• Prefer async/await — Prefer async/await over callbacks or raw promises for cleaner code.
• Output to stdout/stderr — Use console.log() for stdout and console.error() for stderr.
• Let scripts complete naturally — Use process.exit() only when needed.
• Keep it simple — For simple operations, synchronous code is easier to reason about.