invariant

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

Similar packages

Other packages similar to invariant

assert

The 'assert' module is a part of Node.js core and provides a simple set of assertion tests that can be used to test invariants. Unlike 'invariant', which is designed for production use, 'assert' is primarily intended for testing purposes. 'assert' provides a wider range of assertion types, such as deep equality checks, but does not allow for custom error messages in the same way 'invariant' does.

check-types

The 'check-types' npm package offers a rich set of assertions for type checking and is more focused on type validation rather than general invariants. While 'invariant' is used to assert any condition and throw an error if it fails, 'check-types' provides more granular type-specific assertions, such as checking if a value is a string, number, etc. This makes 'check-types' more suitable for validating input types rather than enforcing general program invariants.