babel-plugin-espower

3.0.1 verified Sat Apr 25 auth: no javascript

Babel plugin for power-assert that transforms assertion expressions (assert, assert.ok, assert.equal, etc.) at build time to produce detailed, tree-structured failure messages. Current stable version is 3.0.1 (for Babel 7+). Release cadence is low, driven by power-assert ecosystem updates. Key differentiator: unlike generic assertion libraries, it leverages Babel AST rewriting to embed variable values and expression results into assertion output, enabling richer debugging without runtime instrumentation. Compatible only with Babel 7; separate major versions exist for Babel 6 (2.x) and Babel 5 (1.x).

Common errors

error Error: Cannot find module 'babel-plugin-espower' ↓

cause babel-plugin-espower is not installed or version mismatched with Babel.

fix

Run npm install --save-dev babel-plugin-espower. Ensure Babel version matches: Babel 7 uses v3, Babel 6 uses v2, Babel 5 uses v1.

error AssertionError: expected [...] to deeply equal [...] (no power-assert output) ↓

cause babel-plugin-espower is not applied to the test file, or power-assert import is missing.

fix

Add 'babel-plugin-espower' to your Babel plugins configuration (after presets) and ensure test files import power-assert.

error Error: Plugin or preset file "babel-plugin-espower" is not a function. ↓

cause Using a version of babel-plugin-espower incompatible with your Babel version (e.g., v3 with Babel 6).

fix

Check Babel version: Babel 7 -> babel-plugin-espower@3, Babel 6 -> @2, Babel 5 -> @1.

error TypeError: Cannot read properties of undefined (reading 'type') ↓

cause babel-plugin-espower running before syntax transforms, causing AST nodes to not be fully parsed.

fix

Ensure babel-plugin-espower is listed last in the plugins array, after all presets and other plugins.

Warnings

breaking babel-plugin-espower v3 is incompatible with Babel 6. You must use v2 for Babel 6 and v1 for Babel 5. ↓

fix Use babel-plugin-espower@2 for Babel 6, babel-plugin-espower@1 for Babel 5, or upgrade to Babel 7.

breaking babel-plugin-espower must be applied after all other syntax transforms (e.g., after preset-env) to work correctly. ↓

fix Place 'babel-plugin-espower' last in the plugins array in your Babel config.

gotcha power-assert must be imported in test files for babel-plugin-espower to have effect; the plugin transforms calls to assert, assert.ok, etc. ↓

fix Ensure you have `import assert from 'power-assert'` (or `const assert = require('power-assert')`) in every test file using assert.

deprecated babel-plugin-espower v2 is deprecated for Babel 6 users; actively maintain for Babel 7 only. ↓

fix Upgrade to Babel 7 and use babel-plugin-espower v3.

Install

npm install babel-plugin-espower

yarn add babel-plugin-espower

pnpm add babel-plugin-espower

Imports

default
wrong
```
const espower = require('babel-plugin-espower')
```
correct
```
import espower from 'babel-plugin-espower'
```
Package exports a single function; ESM import is recommended for Babel 7 projects. CJS require works in Node.js but may not be compatible with Babel's plugin resolution across bundlers.
Plugin
wrong
```
plugins: [require('babel-plugin-espower')]
```
correct
```
plugins: ['babel-plugin-espower']
```
In .babelrc or babel.config.js, use the string name. The actual import is rarely needed; Babel resolves strings to the module internally.
Default (Babel API)
wrong
```
babel.transform(code, { plugins: [espower] })
```
correct
```
babel.transform(code, { plugins: ['babel-plugin-espower'] })
```
When using Babel API, the plugin can be specified as a string. The imported function is only needed for advanced usage like custom options (none documented).

Quickstart

Shows a complete example of configuring babel-plugin-espower with Babel 7 and running a mocha test with power-assert.

// Install: npm install --save-dev @babel/core @babel/preset-env babel-plugin-espower power-assert mocha
// Create babel.config.js:
module.exports = {
  presets: [['@babel/preset-env', { targets: { node: 'current' } }]],
  plugins: ['babel-plugin-espower']
};

// test.js
import assert from 'power-assert';
const alice = { name: 'alice' };
const bob = { name: 'bob' };
assert(`${alice.name} and ${bob.name}` === `bob and alice`);

// Run: npx mocha --require @babel/register test.js