node:util

node:util provides MIME parsing, argument and environment-file parsing, text styling, string/array diffs, callback/promise conversion, inspection and formatting, inheritance, deep equality, and type predicates. Default and named imports are available; node:util/types shares the same predicate object as util.types.

import { MIMEType, parseArgs, promisify, styleText } from 'node:util';
import { isUint8Array } from 'node:util/types';

const mime = new MIMEType('text/plain; charset=utf-8');
const { values } = parseArgs({
  args: ['--verbose'],
  options: { verbose: { type: 'boolean' } },
});
const increment = promisify((value, callback) => callback(null, value + 1));
const answer = await increment(41);
const heading = styleText('bold', mime.essence, { validateStream: false });
const bytes = isUint8Array(new Uint8Array([answer]));

The contract targets Node 24.20.0. Portable algorithms run in both QuickJS and StarlingMonkey. The implementation shares deep equality with node:assert, the formatting core with node:console, and scheduling and validation with the existing stream and error helpers.

• parseArgs requires an explicit args array. It never reads host process.argv. parseEnv returns parsed values without modifying an environment.
• styleText requires { validateStream: false } for unconditional ANSI output, or an explicit stream. Stream validation uses its isTTY flag; host color environment variables and terminal capabilities are not consulted.
• TextEncoder and TextDecoder use the engine constructors. StarlingMonkey provides them; QuickJS currently throws ERR_JCO_UNSUPPORTED_NODE_API on construction.
• promisify preserves custom hooks, receivers and callback results. Passing a declared async function without a custom hook throws a deprecated-API error. The shim cannot identify an ordinary function that returns a promise without calling it; use promise-returning functions directly. callbackify schedules callbacks through the shared guest microtask queue, without a separate Node nextTick phase.
• inspect, format and formatWithOptions support ordinary values, collections, descriptors, custom hooks, circular references and inspection options. Native engine details and Node’s full pretty-print layout are not reproduced. Promises display <state unavailable> and weak collections display <items unknown>. showProxy and hidden promise/weak-collection state throw; %o inspects hidden properties without unwrapping proxies. Inspection can trigger proxy traps.
• Buffer, typed-array, boxed-value and collection predicates use intrinsic brand checks. Promise checks require the same realm. Arguments, generator, iterator, module-namespace and function checks use observable tags and can be spoofed; error checks have the same limitation when the engine lacks Error.isError. isCryptoKey requires the engine’s CryptoKey implementation.
• aborted requires the engine’s WeakRef and FinalizationRegistry for an active signal. It uses public abort listeners; an earlier listener calling stopImmediatePropagation() can prevent notification.

Host process and native engine operations throw ERR_JCO_UNSUPPORTED_NODE_API:

• debug/debuglog
• deprecate
• getCallSites
• getSystemErrorName
• getSystemErrorMessage
• getSystemErrorMap
• setTraceSigInt
• convertProcessSignalToExitCode
• transferableAbortController
• transferableAbortSignal
• isProxy, isExternal, and isKeyObject predicates

Deprecated isArray, _extend, _errnoException, and _exceptionWithHostPort throw ERR_JCO_UNSUPPORTED_DEPRECATED_NODE_API.