nodejs-26

name: nodejs-26 description: Node.js 26 (May 2026) runtime conventions — Temporal API enabled by default, V8 14.6 language features (Map.getOrInsert, Iterator.concat), Undici 8 fetch, experimental node:ffi, raw Ed25519 keys, and removals (legacy stream modules, writeHeader, --experimental-transform-types). Use when targeting or upgrading to Node.js 26+.

Apply these conventions when targeting Node.js 26.x (Current line, LTS in October 2026). V8 14.6 / Chromium 146 baseline, NODE_MODULE_VERSION = 147.

Runtime Baseline

V8 14.6.202.33 (from Chromium 146). All V8 14.x ECMAScript additions are available without flags.
Undici 8.0.2 powers fetch, Request, Response, Headers, WebSocket.
ICU 78.3, libuv 1.52.1, bundled SQLite 3.53.x (with Percentile extension), npm 11.x.

Temporal API (enabled by default — no flag)

Available as the global Temporal. Prefer it over Date for any new code that handles time zones, calendars, scheduling, durations, or financial date math.
Core types: Temporal.Instant, Temporal.ZonedDateTime, Temporal.PlainDate, Temporal.PlainTime, Temporal.PlainDateTime, Temporal.PlainYearMonth, Temporal.PlainMonthDay, Temporal.Duration.
Objects are immutable — .add(), .subtract(), .with() return new instances.

Time zones are explicit and first-class — no silent host-tz coercion.

const meeting = Temporal.ZonedDateTime.from('2026-06-15T14:00:00[America/New_York]')
const tomorrow = Temporal.Now.plainDateISO().add({ days: 1 })
const lateBy = Temporal.Duration.from({ minutes: 30 })

Do not rewrite working Date code purely to migrate — use Temporal for new code and migrate strategically.
For DB I/O: instant.toString() produces an ISO 8601 string (RFC 3339 compatible) safe to store in timestamptz. Parse back with Temporal.Instant.from().

V8 14.6 New Language Features

Map / WeakMap upsert (TC39 Stage 4)

map.getOrInsert(key, defaultValue) — return existing or set+return defaultValue.
map.getOrInsertComputed(key, factoryFn) — same, but lazy. factoryFn(key) runs only on miss.

Same methods on WeakMap.

// Replaces the verbose has/get/set dance
const slug = cache.getOrInsertComputed(articleId, buildSlug)

// Grouping / counting
for (const item of items) groups.getOrInsert(item.kind, []).push(item)

Prefer getOrInsertComputed when the default is non-trivial — the factory only fires on a miss, unlike getOrInsert which always evaluates its argument.

Iterator helpers — `Iterator.concat()`

Stage 4 iterator-sequencing proposal. Concatenates any number of iterables into a single iterator without building intermediate arrays.
```
for (const row of Iterator.concat(activeUsers(), pendingUsers(), archivedUsers())) {
  process(row)
}
```
Combine with the existing Iterator.prototype helpers (map, filter, take, drop, flatMap, toArray, reduce, some, every, find) from V8 12.x for fully lazy pipelines.

RegExp.escape (Stage 4)

RegExp.escape(str) safely escapes a string for use inside a regex literal — replaces hand-rolled replace(/[.*+?^${}()|[\]\\]/g, '\\$&') helpers.

Other V8 14.x carry-overs (assume available)

Promise.try(fn), Set set-theory methods (union, intersection, difference, symmetricDifference, isSubsetOf, isSupersetOf, isDisjointFrom), Error.isError, Float16Array, Math.f16round, resizable ArrayBuffer/SharedArrayBuffer, Uint8Array.fromBase64/toBase64/fromHex/toHex.

Standard Library Changes

Undici 8 (powers `fetch`)

Closer alignment with WHATWG Fetch — fewer cross-runtime quirks for streaming, redirect, and abort.
fetch(), WebSocket, EventSource, and Request/Response are all globals — do not import from undici unless you need Dispatcher/Agent/Pool/MockAgent.
For per-call connection pools / proxies, use Agent / ProxyAgent from undici and pass via dispatcher option (Node-specific; not portable to browsers).

Experimental `node:ffi` (added in 26.1.0)

Load native libraries and call symbols directly from JS.
Behind --experimental-ffi flag; under Permission Model also requires --allow-ffi.
Inherently unsafe — invalid pointers, wrong signatures, or use-after-free crash or corrupt the process. Treat like unsafe Rust: isolate behind a typed wrapper, fuzz the boundary.

Crypto

KeyObject import/export now supports 'raw' format for Ed25519 (and other asymmetric primitives where applicable).
Signature operations accept a context option for Ed25519ctx-style domain separation.
module.register() is runtime-deprecated (DEP0218) — migrate ESM loader hooks; will be removed.
DEP0203 and DEP0204 (legacy crypto APIs) are now runtime-deprecated.

Streams / HTTP / misc

localStorage returns undefined when no backing file is configured (previously kept in-memory state silently). Tests relying on the old behavior break.
The bundled SQLite (node:sqlite) enables the Percentile extension.

Removed in 26 (no longer available)

Legacy stream private modules: _stream_readable, _stream_writable, _stream_duplex, _stream_transform, _stream_passthrough, _stream_wrap. Use node:stream exports instead.
http.ServerResponse.prototype.writeHeader() — use writeHead() (note: this removes the typo'd alias only).
--experimental-transform-types flag — use a build step or --experimental-strip-types (which only strips, no transform) for TS execution.
Several older DEP-numbered APIs that had been emitting warnings for multiple majors.

Upgrade Checklist

Rebuild any native add-ons — NODE_MODULE_VERSION bumped to 147.
Search the codebase for imports of _stream_* — replace with node:stream.
Replace response.writeHeader( calls with response.writeHead(.
Remove --experimental-transform-types from start scripts / Dockerfiles.
Audit module.register() callers — migrate to the stable loader-hooks pathway before it is removed.
Replace hand-rolled has/get/set patterns on Map with getOrInsert / getOrInsertComputed.
For new date/time code, prefer Temporal over Date.
Replace polyfilled regexpEscape helpers with RegExp.escape.
If using ESM loaders or worker threads with module.register, plan migration before 27.

Release Cadence Note

Node.js 26 is the Current release; LTS begins October 2026.
Node.js 26 is the last release under the existing odd/even release strategy — from Node.js 27 onward the project adopts a new cadence. Avoid hard-coding assumptions about the old "odd = transient, even = LTS" rule in tooling.