invariant-slim

A simpler version of Facebook's invariant implementation from React.

Installation

invariant-slim is available as an npm package. Simply run npm install invariant-slim command.

To use it in your project:

import invariant from 'invariant-slim'; // ES6 syntax
var invariant = require('invariant-slim'); // ES5 syntax

Usage

Use invariant() to assert state which your program assumes to be true.

Pass in a condition to be evaluated and a format to be displayed as an error message. The format respects the sprintf-style syntax ('%s' will be replaced by whatever arguments are passed in).

Examples:

The following code will not throw:

invariant(
  true,
  'Demo message'
);

The following code will throw with a static message and will output the following error in the console - 'Invariant Violation: A static error message':

invariant(
  false,
  'A static error message'
);

The following code will throw with a dynamic formatted error message and will output the following error in the console - 'Invariant Violation: A dynamic error message arg1,arg2':

invariant(
  false,
  'A dynamic error message %s',
  ['arg1', 'arg2']
);

License

This software is released under the terms of WTFPL v2.0 license.