invariant

A custom Facebook's invariant library which is a way to provide descriptive errors in development but generic errors in production. Here are the changes:

1. In ES6 environment, there is no need to use format which is "/%s/g" stated in source code. As I prefer to use Hello ${username} instead.
2. In some cases, I need to differentiate errors by creating different instance for logging purposes. e.g:

    class ReduxError extends Error {
        ...
    }

Install

With npm do:

npm install typed-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 proces.env. See Server rendering is slower with npm react #812