cli-nodejs-26

name	cli-nodejs-26
description	Node.js 26 (Current) version-specific expertise. Temporal API enabled by default, V8 14.6 (Map/WeakMap.getOrInsert + getOrInsertComputed, Iterator.concat), Undici 8 fetch client, npm 11.x, and semver-major removals (legacy _stream_* modules, http.Server.writeHeader, --experimental-transform-types, module.register runtime-deprecated). WHEN: "Node 26", "Node.js 26", "Temporal", "Temporal.PlainDate", "getOrInsert", "getOrInsertComputed", "Iterator.concat", "Undici 8".
license	MIT
metadata	{"version":"1.0.0"}

Node.js 26 (Current) Version Expert

Node 26 Current. Released May 2026. Will become LTS October 2026, EOL April 2029. This is the last release to follow the existing Current-then-LTS cadence (the schedule changes from Node 27 onward).

Key Features

Feature	Status
Temporal global date/time API	Enabled by default (no flag)
V8 14.6.202.33 (Chromium 146)	Included
Map/WeakMap.prototype.getOrInsert() + getOrInsertComputed()	Added
Iterator.concat()	Added
Undici 8 (fetch)	Updated
npm 11.x bundled	Updated
http.Server.prototype.writeHeader()	Removed (use writeHead())
Legacy _stream_* internal modules	Removed
--experimental-transform-types flag	Removed
module.register()	Runtime-deprecated
NODE_MODULE_VERSION	Bumped to 147 (native addons must rebuild)

Temporal -- Modern Date/Time (No Flag)

Temporal is now a global, enabled by default. It replaces error-prone Date arithmetic with immutable objects, explicit time zones, and predictable math -- ideal for scripts that parse timestamps, compute durations, or schedule work.

// Plain calendar date (no time, no zone)
const date = Temporal.PlainDate.from('2026-05-05');
console.log(date.toString());            // '2026-05-05'
console.log(date.add({ days: 30 }).toString()); // '2026-06-04'
console.log(date.dayOfWeek);             // 2 (Tuesday)

// Date + time, no zone
const dt = Temporal.PlainDateTime.from('2026-05-05T14:30:00');
console.log(dt.add({ hours: 2, minutes: 15 }).toString()); // '2026-05-05T16:45:00'

// Zoned datetime -- explicit, DST-aware
const zoned = Temporal.ZonedDateTime.from('2026-05-05T09:00[America/New_York]');
const inTokyo = zoned.withTimeZone('Asia/Tokyo');
console.log(inTokyo.toString());

// Current instant / now
const now = Temporal.Now.instant();                 // exact time, UTC
const today = Temporal.Now.plainDateISO();          // local calendar date
const zonedNow = Temporal.Now.zonedDateTimeISO('UTC');

// Durations and differences (great for CLI timing / reports)
const start = Temporal.Now.instant();
// ... do work ...
const elapsed = Temporal.Now.instant().since(start);
console.log(elapsed.total('seconds'));              // e.g. 3.142

// Compare two timestamps from logs
const a = Temporal.Instant.from('2026-05-05T10:00:00Z');
const b = Temporal.Instant.from('2026-05-05T10:05:30Z');
console.log(a.until(b).total('minutes'));           // 5.5
console.log(Temporal.Instant.compare(a, b));        // -1

// Convert legacy Date <-> Temporal
const legacy = new Date();
const instant = legacy.toTemporalInstant();         // Date -> Temporal.Instant
const backToDate = new Date(instant.epochMilliseconds);

Script: report file ages with Temporal

import fs from 'node:fs/promises';

const now = Temporal.Now.instant();
const entries = await fs.readdir('.', { withFileTypes: true });

for (const entry of entries.filter(e => e.isFile())) {
  const stat = await fs.stat(entry.name);
  const mtime = stat.mtime.toTemporalInstant();
  const ageDays = now.since(mtime).total({ unit: 'days' });
  console.log(`${entry.name}: ${ageDays.toFixed(1)}d old`);
}

V8 14.6 -- Map/WeakMap Upsert

getOrInsert() and getOrInsertComputed() collapse the read-then-set pattern into one call -- common when grouping, counting, or memoizing in scripts.

// getOrInsert(key, defaultValue) -- returns existing or inserts the default
const counts = new Map();
for (const word of text.split(/\s+/)) {
  counts.set(word, counts.get(word) ?? 0); // old way
}

// New way -- count occurrences
const tally = new Map();
for (const word of text.split(/\s+/)) {
  const n = tally.getOrInsert(word, 0);
  tally.set(word, n + 1);
}

// getOrInsertComputed(key, fn) -- fn runs ONLY when key is absent (lazy)
const cache = new Map();
function expensiveLookup(id) {
  return cache.getOrInsertComputed(id, () => fetchAndParse(id));
}

// Grouping rows by key without the "if not present, create array" dance
const byDept = new Map();
for (const row of rows) {
  byDept.getOrInsertComputed(row.dept, () => []).push(row);
}

// WeakMap variants exist too (object keys, GC-friendly memoization)
const memo = new WeakMap();
const result = memo.getOrInsertComputed(obj, () => compute(obj));

V8 14.6 -- Iterator.concat()

Chain multiple iterators/iterables lazily without materializing arrays -- memory-efficient for large or streamed sequences.

// Lazily iterate several sync sources in sequence (no intermediate arrays)
function* gen() { yield 5; yield 6; }
for (const item of Iterator.concat([1, 2], new Set([3, 4]), gen())) {
  console.log(item); // 1, 2, 3, 4, 5, 6
}

// Walk the keys of several Maps/Sets as one sequence
const a = new Map([['x', 1]]);
const b = new Map([['y', 2]]);
for (const key of Iterator.concat(a.keys(), b.keys())) {
  console.log(key); // 'x', 'y'
}

// Iterator.concat is for synchronous iterators. For async sources
// (e.g. node:fs glob), keep using for-await or Array.fromAsync.

Undici 8 -- Built-in fetch

The global fetch/Request/Response stack moves to Undici 8: tighter WHATWG Fetch alignment, improved request-lifecycle handling, and better streaming/connection management. Existing fetch code keeps working -- no API change required for typical scripting use.

// Streaming a large download with backpressure handled correctly
import { createWriteStream } from 'node:fs';
import { Writable } from 'node:stream';

const res = await fetch('https://example.com/large.bin');
if (!res.ok) throw new Error(`HTTP ${res.status}`);
await res.body.pipeTo(Writable.toWeb(createWriteStream('large.bin')));

npm 11

Node 26 bundles npm 11.x (e.g. 11.13.0). Same major as Node 24 -- faster installs, stricter peer-dependency enforcement, improved lockfile resolution and workspace support. No new migration step versus Node 24 on the npm front.

Removals & Deprecations (semver-major)

These are the breaking changes most likely to bite scripts and tooling:

• http.Server.prototype.writeHeader() removed -- use writeHead().
• Legacy internal stream modules removed -- _stream_readable, _stream_writable, _stream_duplex, _stream_transform, _stream_passthrough, _stream_wrap. Always import from node:stream (these were never public API).
• --experimental-transform-types removed -- use the stable type-stripping support or a build step.
• module.register() runtime-deprecated -- emits a runtime warning; plan to migrate custom loader registration.
• Crypto/stream deprecations promoted to runtime (DEP0201, DEP0203, DEP0204).
• localStorage without a backing file now returns undefined instead of throwing.

Platform/build requirements (for native addons & CI)

• NODE_MODULE_VERSION bumped to 147 -- native modules (better-sqlite3, bcrypt, etc.) must be rebuilt/reinstalled for Node 26.
• GCC requirement raised to 13.2; Python 3.9 dropped from the build toolchain; Windows SDK updated to 11.

Migration Notes

When migrating from Node 24 to Node 26:

• Temporal is available globally -- replace fragile Date arithmetic and ad-hoc timezone math; remove polyfills like @js-temporal/polyfill.
• Use Map/WeakMap.getOrInsert() / getOrInsertComputed() to simplify counting, grouping, and lazy-memoization helpers.
• Use Iterator.concat() to chain iterators instead of spreading into intermediate arrays.
• Audit for removed APIs: replace writeHeader() with writeHead(), and any require('_stream_*') with node:stream imports.
• Drop the --experimental-transform-types flag from scripts/CI.
• Rebuild native dependencies (NODE_MODULE_VERSION 147) -- delete node_modules and reinstall, or rerun npm rebuild, after upgrading.
• Note the release-cadence change: Node 26 is the last version on the current Current→LTS schedule (Node 27+ differs) -- confirm your LTS upgrade plan accordingly.