https://github.com/zertosh/invariant

invariant
https://github.com/zertosh/invariant

Last synced: about 18 hours ago
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invariant

• Host: GitHub
• URL: https://github.com/zertosh/invariant
• Owner: zertosh
• License: mit
• Created: 2014-09-24T04:47:25.000Z (about 10 years ago)
• Default Branch: master
• Last Pushed: 2021-12-14T00:53:36.000Z (almost 3 years ago)
• Last Synced: 2024-10-29T15:04:04.835Z (about 1 month ago)
• Language: JavaScript
• Size: 27.3 KB
• Stars: 1,219
• Watchers: 7
• Forks: 70
• Open Issues: 16
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGELOG.md
  • License: LICENSE

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README

        
# invariant

[![Build Status](https://travis-ci.org/zertosh/invariant.svg?branch=master)](https://travis-ci.org/zertosh/invariant)

A mirror of Facebook's `invariant` (e.g. [React](https://github.com/facebook/react/blob/v0.13.3/src/vendor/core/invariant.js), [flux](https://github.com/facebook/flux/blob/2.0.2/src/invariant.js)).

A way to provide descriptive errors in development but generic errors in production.

## Install

With [npm](http://npmjs.org) do:

```sh

npm install invariant

```

## `invariant(condition, message)`

```js

var invariant = require('invariant');

invariant(someTruthyVal, 'This will not throw');

// No errors

invariant(someFalseyVal, 'This will throw an error with this message');

// Error: Invariant Violation: This will throw an error with this message

```

**Note:** When `process.env.NODE_ENV` is not `production`, the message is required. If omitted, `invariant` will throw regardless of the truthiness of the condition. When `process.env.NODE_ENV` is `production`, the message is optional – so they can be minified away.

### Browser

When used with [browserify](https://github.com/substack/node-browserify), it'll use `browser.js` (instead of `invariant.js`) and the [envify](https://github.com/hughsk/envify) transform will inline the value of `process.env.NODE_ENV`.

### Node

The node version is optimized around the performance implications of accessing `process.env`. The value of `process.env.NODE_ENV` is cached, and repeatedly used instead of reading `process.env`. See [Server rendering is slower with npm react #812](https://github.com/facebook/react/issues/812)