chrishuffman5/cli-nodejs-20

Node.js 20 LTS Version Expert

Node 20 LTS (codename Iron). Released April 2023, EOL April 2026. This is the widest-deployed LTS version.

Key Features

| Feature | Status | |---|---| | node:test built-in test runner | Stable | | fetch / Request / Response | Stable | | Permission model (--allow-fs-read, etc.) | Experimental | | Single Executable Applications (SEA) | Experimental | | --watch mode | Stable | | import.meta.resolve() | Stable | | V8 11.3, Array.fromAsync() | Included |

Built-in Test Runner (node:test)

import { test, describe, it, before, after, mock } from 'node:test';
import assert from 'node:assert/strict';

// Simple test
test('addition works', () => {
  assert.strictEqual(1 + 1, 2);
});

// Async test
test('fetch returns data', async () => {
  const res = await fetch('https://jsonplaceholder.typicode.com/todos/1');
  assert.ok(res.ok);
  const data = await res.json();
  assert.equal(data.id, 1);
});

// Test suite with describe/it
describe('Array', () => {
  it('should support map', () => {
    assert.deepStrictEqual([1, 2, 3].map(x => x * 2), [2, 4, 6]);
  });

  it('should support filter', () => {
    assert.deepStrictEqual([1, 2, 3, 4].filter(x => x > 2), [3, 4]);
  });
});

// Mocking
test('mocked function', () => {
  const fn = mock.fn(() => 42);
  assert.equal(fn(), 42);
  assert.equal(fn.mock.calls.length, 1);
});

# Run tests
node --test                              # find and run **/*.test.{js,mjs}
node --test src/                         # test files in directory
node --test --watch                      # watch mode
node --test --test-reporter=spec         # spec reporter
node --test --test-reporter=tap          # TAP output
node --test --test-concurrency=4         # parallel

Permission Model

# Sandbox: restrict file system, network, child_process
node --experimental-permission --allow-fs-read=/data --allow-fs-write=/tmp script.mjs
node --experimental-permission --allow-child-process --allow-net script.mjs

# No flags = deny all (when --experimental-permission is set)
node --experimental-permission script.mjs  # all restricted

Permission flags: --allow-fs-read, --allow-fs-write, --allow-child-process, --allow-worker, --allow-net.

Watch Mode

node --watch server.mjs              # restart on file changes
node --watch-path=./src server.mjs   # watch specific directory
node --watch --test                   # rerun tests on changes

Stable fetch API

fetch, Request, Response, Headers, FormData are all globally available without import.

const res = await fetch('https://api.example.com/data');
const data = await res.json();

Single Executable Applications (SEA)

# 1. Create SEA config
echo '{"main":"app.js","output":"sea-prep.blob"}' > sea-config.json

# 2. Generate the blob
node --experimental-sea-config sea-config.json

# 3. Copy node binary and inject
cp $(which node) my-app
npx postject my-app NODE_SEA_BLOB sea-prep.blob --sentinel-fuse NODE_SEA_FUSE_fce680ab2cc467b6e072b8b5df1996b2

# 4. Run standalone
./my-app

V8 11.3 Highlights

• Array.fromAsync() -- async version of Array.from()
• ArrayBuffer.prototype.transfer() -- zero-copy transfer
• String .isWellFormed() and .toWellFormed() -- Unicode validation

Migration Notes

When migrating from Node 18 to Node 20:

• fetch moves from experimental to stable
• node:test moves from experimental to stable
• --watch moves from experimental to stable
• import.meta.resolve() becomes synchronous
• Default OpenSSL updated to 3.0.x