node-invariant

Yet another assertion library.

Installation

You can install this library via npm:

$ npm i @zheltikov/node-invariant

Usage

The main function to be used in this library is invariant. This function is intended to indicate a programmer error for a condition that should never occur, similar to assertions. For example:

import { invariant } from '@zheltikov/node-invariant';

const obj = new Date();
invariant(obj instanceof Date, 'Object must have type Date');

const p = 123;
invariant(p !== null, 'Value can\'t be null');

const max = 100;
invariant(p !== null && p <= max, 'p\'s value %d must be <= %d', p, max);

If the first argument value evaluates to true, the program continues execution; otherwise, the function invariant_violation is called. That function either throws an InvariantException, or calls the handler previously registered by the function invariant_callback_register.

The first argument is evaluated as a boolean expression. The second argument is a string that can contain text and/or optional formatting information as understood by the function sprintf. The optional comma-separated list of values following the string must match the set of types expected by the optional formatting information inside that string.

TODO

• [X] Build a functional-style assertion library
• [ ] Build an object-oriented interface for these functions