Sign inDemoInstall


Package Overview
File Explorer

Advanced tools

Install Socket

Protect your apps from supply chain attacks



A ridiculously light-weight argument validator (now browser friendly)


Version published
Weekly downloads
increased by3.67%

Weekly downloads

Package description

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


Other packages similar to 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:

*matches any type
AArray.isArray OR an arguments object
Stypeof == string
Ntypeof == number
Ftypeof == function
Otypeof == object and not type A and not type E
Btypeof == boolean
Einstanceof 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.



Last updated on 22 May 2018

Did you know?

Socket installs a GitHub app to automatically flag issues on every pull request and report the health of your dependencies. Find out what is inside your node modules and prevent malicious activity before you update the dependencies.


Related posts

SocketSocket SOC 2 Logo


  • Package Alerts
  • Integrations
  • Docs
  • Pricing
  • FAQ
  • Roadmap

Stay in touch

Get open source security insights delivered straight into your inbox.

  • Terms
  • Privacy
  • Security

Made with ⚡️ by Socket Inc