assert-plus

What is assert-plus?

The assert-plus npm package is a library that provides a set of assertion functions for verifying invariants. It is an extension of the built-in assert module in Node.js, offering more specific assertion types and better error messages. It is commonly used to enforce type checking and value validation in JavaScript code, particularly on the server side with Node.js.

What are assert-plus's main functionalities?

Type assertions

Asserts that the given argument is of the expected type. If the argument is not of the specified type, it throws a TypeError with a message indicating the name of the argument and the expected type.

const assert = require('assert-plus');
assert.string('hello', 'argument'); // OK
assert.string(123, 'argument'); // Throws TypeError

Value assertions

Asserts that the given argument is of the expected type or is undefined/null if it is an optional argument. If the argument is provided and is not of the specified type, it throws a TypeError.

const assert = require('assert-plus');
assert.optionalNumber(null, 'optionalArgument'); // OK
assert.optionalNumber('not a number', 'optionalArgument'); // Throws TypeError

Array content assertions

Asserts that the given argument is an array where every element is of the expected type. If any element is not of the specified type, it throws a TypeError.

const assert = require('assert-plus');
assert.arrayOfString(['hello', 'world'], 'stringArray'); // OK
assert.arrayOfString(['hello', 123], 'stringArray'); // Throws TypeError

Other packages similar to assert-plus

chai

Chai is a BDD / TDD assertion library for node and the browser that can be delightfully paired with any javascript testing framework. It offers a richer and more flexible API compared to assert-plus, including chainable assertions and a variety of plugins.

expect.js

Expect.js is a minimalistic BDD-style assertions library that can be used in Node.js or in the browser. It provides a similar set of assertions as assert-plus but with a different syntax and less strict type checking.

README

node-assert-extra

This library is a super small wrapper over node's assert module that has two things: (1) the ability to disable assertions with the environment variable NODE_NDEBUG, and (2) some API wrappers for argument testing. Like assert.string(myArg, 'myArg'). As a simple example, most of my code looks like this:

var assert = require('assert-plus');

function fooAccount(options, callback) {
    assert.object(options, 'options');
	assert.number(options.id, 'options.id);
	assert.bool(options.isManager, 'options.isManager');
	assert.string(options.name, 'options.name');
	assert.arrayOfString(options.email, 'options.email');
	assert.func(callback, 'callback');

    // Do stuff
	callback(null, {});
}

API

All methods that aren't part of node's core assert API are simply assumed to take an argument, and then a string 'name' that's not a message; AssertionError will be thrown if the assertion fails with a message like:

AssertionError: foo (string) is required
at test (/home/mark/work/foo/foo.js:3:9)
at Object.<anonymous> (/home/mark/work/foo/foo.js:15:1)
at Module._compile (module.js:446:26)
at Object..js (module.js:464:10)
at Module.load (module.js:353:31)
at Function._load (module.js:311:12)
at Array.0 (module.js:484:10)
at EventEmitter._tickCallback (node.js:190:38)

from:

function test(foo) {
    assert.string(foo, 'foo');
}

There you go. You can check that arrays are of a homogenous type with Arrayof$Type:

function test(foo) {
    assert.arrayOfString(foo, 'foo');
}

You can assert IFF an argument is not undefined (i.e., an optional arg):

assert.optionalString(foo, 'foo');

Lastly, you can opt-out of assertion checking altogether by setting the environment variable NODE_NDEBUG=1. This is pseudo-useful if you have lots of assertions, and don't want to pay typeof () taxes to v8 in production.

The complete list of APIs is:

• assert.bool
• assert.buffer
• assert.func
• assert.number
• assert.object
• assert.string
• assert.arrayOfBool
• assert.arrayOfFunc
• assert.arrayOfNumber
• assert.arrayOfObject
• assert.arrayOfString
• assert.optionalBool
• assert.optionalBuffer
• assert.optionalFunc
• assert.optionalNumber
• assert.optionalObject
• assert.optionalString
• assert.optionalArrayOfBool
• assert.optionalArrayOfFunc
• assert.optionalArrayOfNumber
• assert.optionalArrayOfObject
• assert.optionalArrayOfString
• assert.AssertionError
• assert.fail
• assert.ok
• assert.equal
• assert.notEqual
• assert.deepEqual
• assert.notDeepEqual
• assert.strictEqual
• assert.notStrictEqual
• assert.throws
• assert.doesNotThrow
• assert.ifError

Installation

npm install assert-plus

License

The MIT License (MIT) Copyright (c) 2012 Mark Cavage

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Bugs

See https://github.com/mcavage/node-assert-plus/issues.