aproba

What is aproba?

The aproba package is a lightweight argument validation library for Node.js. It allows developers to assert types and values of arguments in functions, ensuring that the functions are called with the expected arguments. This can help catch bugs early in the development process by providing a simple and concise way to validate function inputs.

What are aproba's main functionalities?

Type validation

This feature allows you to validate the types of arguments passed to a function. In the code sample, 'N' stands for number and 'S' for string, ensuring the first argument is a string and the second is a number.

"use strict";
const A = require('aproba');

function exampleFunction(a, b) {
  A('NS', arguments);
  // Function logic here
}

exampleFunction('hello', 123);

Optional arguments

aproba supports optional arguments in its type validation. In the example, the '?' after 'S' indicates that the second argument is optional. This means the function can be called with just the first argument.

"use strict";
const A = require('aproba');

function exampleFunction(a, b) {
  A('NS?', arguments);
  // Function logic here
}

exampleFunction('hello');

Other packages similar to aproba

joi

Joi is a powerful object schema description language and validator for JavaScript objects. Compared to aproba, Joi offers a more extensive set of features for validating complex object structures and custom types, making it suitable for more complex validation scenarios.

validate.js

validate.js provides a declarative way of validating javascript objects. It is similar to aproba in its purpose of validating function arguments but offers a different API and additional features for validating objects against predefined constraints and custom validation functions.

yup

Yup is a JavaScript schema builder for value parsing and validation. It defines a schema with a more expressive and less verbose syntax compared to aproba. Yup allows for more complex validations, including nested objects and arrays, making it a more versatile choice for data validation.

README

aproba

A ridiculously light-weight function argument validator

var validate = require("aproba")

function myfunc(a, b, c) {
  // `a` must be a string, `b` a number, `c` a function
  validate('SNF', arguments) // [a,b,c] is also valid
}

myfunc('test', 23, function () {}) // ok
myfunc(123, 23, function () {}) // type error
myfunc('test', 23) // missing arg error
myfunc('test', 23, function () {}, true) // too many args error

Valid types are:

type	description
*	matches any type
A	Array.isArray OR an arguments object
S	typeof == string
N	typeof == number
F	typeof == function
O	typeof == object and not type A and not type E
B	typeof == boolean
E	instanceof Error OR null (special: see below)
Z	== null

Validation failures throw one of three exception types, distinguished by a code property of EMISSINGARG, EINVALIDTYPE or ETOOMANYARGS.

If you pass in an invalid type then it will throw with a code of EUNKNOWNTYPE.

If an error argument is found and is not null then the remaining arguments are optional. That is, if you say ESO then that's like using a non-magical E in: E|ESO|ZSO.

But I have optional arguments?!

You can provide more than one signature by separating them with pipes |. If any signature matches the arguments then they'll be considered valid.

So for example, say you wanted to write a signature for fs.createWriteStream. The docs for it describe it thusly:

fs.createWriteStream(path[, options])

This would be a signature of SO|S. That is, a string and and object, or just a string.

Now, if you read the full fs docs, you'll see that actually path can ALSO be a buffer. And options can be a string, that is:

path <String> | <Buffer>
options <String> | <Object>

To reproduce this you have to fully enumerate all of the possible combinations and that implies a signature of SO|SS|OO|OS|S|O. The awkwardness is a feature: It reminds you of the complexity you're adding to your API when you do this sort of thing.

Browser support

This has no dependencies and should work in browsers, though you'll have noisier stack traces.

Why this exists

I wanted a very simple argument validator. It needed to do two things:

1. Be more concise and easier to use than assertions

2. Not encourage an infinite bikeshed of DSLs

This is why types are specified by a single character and there's no such thing as an optional argument.

This is not intended to validate user data. This is specifically about asserting the interface of your functions.

If you need greater validation, I encourage you to write them by hand or look elsewhere.