About

A dependency-free isomorphic port of the Node.js API require("node:util").inspect(). Works on any ES6 JS runtime, as it has no dependency on V8 or Node.js. Can be used in the browser, in React Native, etc.

Usage

Install as follows:

npm install util-inspect-isomorphic

Use just like the original (see the official Node.js docs for full details):

import { inspect } from "util-inspect-isomorphic";

// Serialise Errors with cause:
console.error(inspect(new Error("Outer", { cause: new Error("Inner") })));

// Inspect deeply-nested objects:
console.log(inspect({ a: { b: { c: { d: {} } } } }), { depth: null });

// Print with colours:
console.log(inspect(["wow", new Date(), true], { colors: true }));

// Insert an underscore between every 3 digits:
console.log(inspect(1000000000, { numericSeparator: true }));

Engine support

Requires ES6 and ESM support (or a bundler that can downlevel them).

Differences from the original

This library is a port of the Node.js core code in lib/internal/util/inspect.js (and any dependent files) as it was in main on June 2025, so approximately Node.js v24.1.0. Here are the main compromises that had to be made in the port:

• Proxy types cannot be inspected, so showProxy: true has no effect. Instead of the Proxy itself, the Proxy target will be inspected.
• For external (cross-realm, etc.) types, we cannot print the memory address, so just print [External: <address unknown>].
• Limited Promise introspection – we can't tell whether it is <pending>, <rejected>, or resolved, so we write <uninspectable> instead.
• Type inspection can be fooled, as it doesn't use engine-level introspection.
• Not all types of TypedArray get special handling. Namely Float16Array, BigInt64Array, and BigUint64Array.
• Does not apply special colour-highlighting to stack trace lines that enter node_modules or Node.js core modules.

Sources

Here's a file-by-file summary of what was adapted from the Node.js internals or other projects:

• src/index.ts:
  • lib/internal/util.js
• src/inspect.ts:
  • lib/internal/util/inspect.js
• src/internal-assert.ts:
  • lib/internal/assert.js
• src/internal-errors.ts:
  • lib/internal/errors.js
• src/internal-util-types.ts:
  • lib/internal/util/types.js
  • Some code adapted from node-inspect-extracted, as per the code comments.
• src/internal-util.ts:
  • lib/internal/util.js
• src/internal-validators.ts:
  • lib/internal/validators.js
• src/primordials.ts:
  • node-primordials, itself a TypeScript port of lib/internal/per_context/primordials.js
• src/node-util.ts:
  • src/node_util.cc
  • Some code adapted from node-inspect-extracted, as per the code comments.

See also

I found out about the excellent node-inspect-extracted only after largely finishing this port. There are a few differences between our approaches.

• node-inspect-extracted:
  • is a CommonJS library, written in JavaScript.
  • is designed to be easy to keep up to date with upstream, whereas util-inspect-isomorphic is a one-time snapshot.
  • has some tests.
• util-inspect-isomorphic:
  • is a port to ESM, written in TypeScript.
  • is confirmed to work in React Native.
    • I found that I had to change calls such as const { Object } = primordials to primordials.Object to get it to run. I can't be sure whether it was a Hermes runtime issue or a Metro bundling issue.
  • is untested. Use at your own risk!

Contributing

# Clone the repo
git clone [email protected]:shirakaba/util-inspect-isomorphic.git
cd util-inspect-isomorphic

# Install the dev dependencies
npm install

# Build the code from TypeScript to JavaScript
npm run build

# Test the code (e.g. by making a new script)
node ./scripts/test.js