This file contains ambiguous Unicode characters that may be confused with others in your current locale. If your use case is intentional and legitimate, you can safely ignore this warning. Use the Escape button to highlight these characters.
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
varinvariant=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)