invariant

A mirror of Facebook's invariant (e.g. React, flux).

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

Install

With npm do:

npm install invariant

invariant(condition, message)

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, it'll use browser.js (instead of invariant.js) and the 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

2.2.4 / 2018-03-13

• Use flow strict mode (i.e. @flow strict).

2.2.3 / 2018-02-19

• Change license from BSD+Patents to MIT.

2.2.2 / 2016-11-15

• Add LICENSE file.
• Misc housekeeping.

2.2.1 / 2016-03-09

• Use NODE_ENV variable instead of __DEV__ to cache process.env.NODE_ENV.

2.2.0 / 2015-11-17

• Use error.name instead of Invariant Violation.

2.1.3 / 2015-11-17

• Remove @provideModule pragma.

2.1.2 / 2015-10-27

• Fix license.

2.1.1 / 2015-09-20

• Use correct SPDX license.
• Test "browser.js" using browserify.
• Switch from "envify" to "loose-envify".

2.1.0 / 2015-06-03

• Add "envify" as a dependency.
• Fixed license field in "package.json".

2.0.0 / 2015-02-21

• Switch to using the "browser" field. There are now browser and server versions that respect the "format" in production.

1.0.2 / 2014-09-24

• Added tests, npmignore and gitignore.
• Clarifications in README.

1.0.1 / 2014-09-24

• Actually include 'invariant.js'.

1.0.0 / 2014-09-24

• Initial release.