loupe

library1.3.1jsnpmunverified

Loupe is a robust, cross-platform utility for converting JavaScript objects into string representations, designed to work consistently in both Node.js and browser environments. It provides functionality similar to Node.js' built-in `util.inspect()`, making it a valuable tool for debugging and generating human-readable output of complex data structures. The current stable major version is `4.x`, with `v4.0.0` introducing significant breaking changes regarding custom inspection methods. The package maintains a moderate release cadence, with minor and patch updates preceding major version increments, reflecting ongoing development and refinement. As a core component within the Chai.js assertion library ecosystem, Loupe's key differentiator is its unified inspection behavior across diverse JavaScript runtimes, addressing the common challenge of inconsistent object serialization.

testing serialization

npm install loupe

github ↗package ↗

INSTALL

IMPORT

SIG · LOUPE

loupe

testingjavascriptv1.3.1

Install

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Import

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Disk

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Pass rate

0/ 6

Env Coverage0 / 6

glibc

18–22

musl

18–22

Install & Compatibility

Where this runs

tested against v? · npm install

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

node 18–226 runs

build_error

glibc

node 18–226 runs

build_error

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

inspect

✓ import { inspect } from 'loupe';

✗ import loupe from 'loupe'; // then `loupe.inspect` is correct, but direct destructuring is preferred

The primary `inspect` function is a named export. Default imports are not recommended for direct inspection.

inspect

✓ const { inspect } = require('loupe');

✗ const inspect = require('loupe'); // Then `inspect.inspect` would be needed, or a TypeError if called directly

CommonJS environments should use destructuring for the `inspect` function as it's a named export.

Custom inspection

✓ obj[Symbol('nodejs.util.inspect.custom')] = function() { /* ... */ };

✗ obj.inspect = function() { /* ... */ };

Since v4.0.0, custom inspect methods must use `Symbol('nodejs.util.inspect.custom')` or `Symbol('chai/inspect')` rather than a plain `.inspect` property for compatibility and best practices.

Demonstrates how to import and use the `inspect` function with various data types, including objects, arrays, dates, regexes, functions, and a custom-inspectable object (v4.x style).

import { inspect } from 'loupe'; // Basic types console.log(inspect({ foo: 'bar', baz: 123 })); console.log(inspect([1, 'two', { three: 3 }])); console.log(inspect(new Date('2023-01-15T10:00:00Z'))); console.log(inspect(/pattern/gi)); // Functions function greet(name) { return `Hello, ${name}`; } console.log(inspect(greet)); // Complex objects with custom inspection (v4.x compatible) const customInspectable = { value: 'secret', [Symbol('nodejs.util.inspect.custom')]: function(depth, opts) { return `CustomObject { value: '${this.value.slice(0, 3)}...' }`; } }; console.log(inspect(customInspectable)); // Errors and Promises const error = new Error('Something went wrong'); console.log(inspect(error)); console.log(inspect(Promise.resolve(42)));

Debug

Known issues

breakingVersion 4.0.0 removed support for custom inspection methods defined via a plain `.inspect` property on objects.

fix

Migrate custom inspect functions to use `Symbol('nodejs.util.inspect.custom')` or `Symbol('chai/inspect')` instead. This aligns with Node.js' `util.inspect` behavior.

affects: >=4.0.0

gotchaWhen inspecting very large or deeply nested objects, the output can become excessively long and impact performance or readability.

fix

Loupe's `inspect` function accepts options for controlling depth and truncation. Consider using `inspect(obj, { depth: 2, maxLineLength: 80 })` to limit output size.

affects: >=3.0.0

gotchaThe `loupe` package outputs declaration maps ('.d.ts.map' files) prior to v4.0.0, which were then removed in v4.0.0.

fix

No direct fix needed, but be aware of changes in build output if you were relying on these declaration maps for debugging or tooling purposes in older versions. For v4.0.0+, declaration maps are no longer shipped.

affects: <4.0.0

Errors

Common errors & fixes

TypeError: inspect is not a function

Attempting to call `require('loupe')` or `import loupe from 'loupe'` directly as a function, without destructuring the `inspect` named export.

fix

Use named import `import { inspect } from 'loupe';` for ESM or destructuring `const { inspect } = require('loupe');` for CommonJS.

Custom inspection logic not being invoked for my object.

Using a plain `.inspect` property for custom inspection logic on an object, which was deprecated and removed in v4.0.0.

fix

For `loupe` v4.0.0 and above, custom inspect methods must be defined using the `Symbol('nodejs.util.inspect.custom')` or `Symbol('chai/inspect')` symbol keys. Example: `obj[Symbol('nodejs.util.inspect.custom')] = function() { /* ... */ };`

Upgrade

Version history

1.3.1latest on npm

Audit

Dependencies

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Agent activity

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node

Resources

githubhttps://github.com/chaijs/loupe ↗

packagehttps://www.npmjs.com/package/loupe ↗