Registry / testing / assertion-error-formatter

assertion-error-formatter

library3.0.0jsnpmunverified

Formats JavaScript Error objects into human-readable diff output (actual vs expected) for testing frameworks. Version 3.0.0 is ESM-only, released 2022-01-31, no longer supports CJS require(). Extracted from Mocha, provides customizable color functions and inline/unified diff styles. Lightweight (0 dependencies), focused on assertion error display, not assertions themselves.

testing

npm install assertion-error-formatter

github ↗package ↗homepage ↗

INSTALL

IMPORT

SIG · ASSERTION-ERROR-FO

assertion-error-formatter

testingjavascriptv3.0.0

harness data pending

Install & Compatibility

Where this runs

No compatibility data collected yet for this library.

Code

Verified usage

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

format

✓ import { format } from 'assertion-error-formatter'

✗ const { format } = require('assertion-error-formatter')

Version 3 is ESM-only; CJS require() will throw. Use dynamic import if CJS is required.

default import (format)

✓ import format from 'assertion-error-formatter'

✗ const format = require('assertion-error-formatter')

As of v3, namespace default export is not available; use named import { format }.

type ColorFns

✓ import type { ColorFns } from 'assertion-error-formatter'

✗ import { ColorFns } from 'assertion-error-formatter'

Type import only for TypeScript, not a runtime value.

Shows basic usage: import format, create an error with actual/expected, call format with options, and output the diff.

import { format } from 'assertion-error-formatter'; const error = new Error('assertion failed'); error.actual = { foo: 'bar' }; error.expected = { foo: 'baz' }; const formatted = format(error, { colorFns: { diffAdded: (s) => s, diffRemoved: (s) => s, errorMessage: (s) => s, errorStack: (s) => s }, inlineDiff: false }); console.log(formatted);

Debug

Known issues

breakingVersion 3 drops CommonJS support; require() will throw MODULE_NOT_FOUND or ERR_REQUIRE_ESM.

fix

Use dynamic import() or migrate to ESM.

affects: >=3.0.0

breakingDefault export removed in v3; only named export { format } is available.

fix

Change import from 'assertion-error-formatter' to { format }.

affects: >=3.0.0

gotchaThe error object must have 'actual' and 'expected' properties; otherwise the formatted string may be empty or unhelpful.

fix

Ensure error.actual and error.expected are set before formatting.

affects: *

Errors

Common errors & fixes

SyntaxError: Cannot use import statement outside a module

Running ESM code in a CommonJS context without type:"module" or .mjs extension.

fix

Add "type": "module" to package.json or rename file to .mjs.

ERR_REQUIRE_ESM: require() of ES Module /path/to/assertion-error-formatter/index.js not supported.

Using require() to load an ESM-only package.

fix

Use dynamic import(): const { format } = await import('assertion-error-formatter');

TypeError: format is not a function

Importing as default instead of named import.

fix

Use import { format } from 'assertion-error-formatter'.

Upgrade

Version history

3.0.0latest on npm

Audit

Dependencies

No dependency data recorded yet.

Agent activity

24 hits · last 30 days

node

Amazon

OpenAI (training)

Resources

githubhttps://github.com/charlierudolph/node-assertion-error-formatter ↗

packageassertion-error-formatter ↗

homepagehttps://github.com/charlierudolph/node-assertion-error-formatter ↗