gubu

Gubu: An object shape validation utility.

Quick Example | Common Use Cases | Install and Usage | Shape Rules | API

NOTE: WORK IN PROGRESS

This is a schema validator in the tradition of Joi or any JSON-Schema validator, with the key features:

• Schemas are WYSIWYG - you define a schema with a template matching your object structure;
• The most useful cases are the easiest to specify (e.g. optional defaults are just literal values);
• The implementation is iterative (a depth-first loop over the property tree) not recursive, so it's nice and fast and can handle any size of data and schema.

Why write yet another validator? I've used Joi for a long time, but always found its schema definition a little verbose at the syntax level. I've never liked JSON-Schema - it's just too noisy to eyeball. What I do like is Vue.js property validation, but that only works at the top level. I did write a prototype deep Vue property validator using Joi, but it's pretty clunky.

This validator is motivated by two use cases: adding message validation to the Seneca microservices framework, and providing deep defaults for complex custom Vue.js components. I think it does both jobs rather nicely with an easy-to-read syntax.

	This open source module is sponsored and supported by Voxgig.

Quick Example

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const { Gubu } = require('gubu')

// Property a is optional, must be a Number, and defaults to 1.
// Property b is required, and must be a String.
const shape = Gubu({ a: 1, b: String })

// Object shape is good! Prints `{ a: 99, b: 'foo' }`
console.log( shape({ a: 99, b: 'foo' }) )

// Object shape is also good. Prints `{ a: 1, b: 'foo' }`
console.log( shape({ b: 'foo' }) )

// Object shape is bad. Throws an exception with message:
//   Validation failed for path "a" with value "BAD" because the value is not of type number.
//   Validation failed for path "b" with value "" because the value is required.'
console.log( shape({ a: 'BAD' }) )

As shown above, you use the exported Gubu function to create a validation checker (does the argument match the schema shape?). If valid, the checker returns its first argument, otherwise it throws an exception listing all (not just the first!) the validity errors.

Common Use Cases

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Option defaults and validation

Let's say you have a server that needs to run on a given host and port, but by default should run on localhost on port 8080. The host should be a non-empty string, and the port should be a number.

const optionShape = Gubu({
  host: 'localhost',
  port: 8080
})

// These print: { host: 'localhost', port: 8080 }
console.log(optionShape())
console.log(optionShape({}))

// Prints: { host: 'localhost', port: 9090 }
console.log(optionShape({ port: 9090 }))

// All of these throw an error.
console.log(optionShape({ host: 9090 }))   // Not a string.
console.log(optionShape({ port: '9090' })) // Not a number.
console.log(optionShape({ host: '' }))     // Not really a usable string!

Deep structures

You're building a front end component that displays data from the back end, and you want to handle bad data gracefully.

const productListShape = Gubu({
  view: {
    discounts: [
      // All elements must match this shape.
      { 
        name: String, 

        // A custom validation!
        percent: (v: any) => 0 < v && v < 100 
      }
    ],
    products: [
      { 
        name: String, 
        price: Number, 
      }
    ]
  }
})


// Oh noes! The back end gave me nothing! Luckily I can still work with a
// valid, if empty, data structure.

productListShape({}) // returns:
{ view: { discounts: [], products: [] } }

Install

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$ npm install gubu

Usage

The Gubu module has no dependencies. A single function named Gubu is exported. Utility functions are provided as properties of Gubu or can be exported separately.

TypeScript

Gubu is written in TypeScript, and can be imported naturally:

import { Gubu } from 'gubu' 

Types are provided in gubu.d.ts.

Browser

A minified version is provided as gubu.min.js, which can be directly loaded into a web page and exports a Gubu global object.

However you're probably better off importing this module in the usual manner for your build process and bundling it together with everything else.

Shape Rules

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The general principle of Gubu's design is that the schema shape should match a valid object or value as closely as possible.

For scalar values you can provide a native type object to make the value required:

• Gubu(String) matches strings: 'foo'
• Gubu(Number) matches numbers: 123
• Gubu(Boolean) matches booleans: true

Or defaults to make the value optional:

• Gubu('bar') matches strings: 'foo', and undefined
• Gubu(0) matches numbers: 123, and undefined
• Gubu(false) matches booleans: true, and undefined

If a value is optional and undefined, the default value is returned: Gubu('bar')() returns 'bar'.

The values null and NaN must match exactly. The value undefined is special - it literally means no value.

Empty strings are not considered to be valid if a string is required (this is usually what you want). To allow empty string, use Gubu(Empty(String)) (where Empty is exported by the Gubu module).

For objects, write them as you want them:

let shape = Gubu({
  foo: {
    bar: {
      zed: String,
      qaz: Number,
    }
  }
})

The above shape will match:

{
  foo: {
    bar: {
      zed: 'x',
      qaz: 1
    }
  }
}

For arrays, the first elements is treated as the shape that all elements in the array must match:

• Gubu([String]) matches ['a', 'b', 'c']
• Gubu([{x:1}]) matches [{x: 11}, {x: 22}, {x: 33}]

If you need specific elements to match specific shapes, add these shapes after the first element:

• Gubu([String,Number]) matches [1, 'b', 'c'] - the first element is a Number, the rest Strings.

Thus, the element 0 of a shape array defines the general element, and following elements define special cases (offset by 1).

You can specify custom validation using functions:

• Gubu({a: (v) => 10<v }): matches {a: 11} as 10 < 11

And you can manipulate the value if you need to:

• Gubu({a: (v,u) => 10<v ? (u.val=2*v, true) : false }): matches {a: 11} as 10 < 11 and returns {a: 22}.

You can also compose validations together:

const shape = Gubu({ a: Gubu({ x: Number }) })

// Matches { a: { x: 1 } } as expected
shape({ a: { x: 1 } })

Gubu exports shape "builder" utility functions that let you further refine the shape (You've already seen the Empty builder above that allows strings to be empty). You wrap your value with the builder function to apply the desired effect.

The Required builder makes a value required:

const { Gubu, Required } = require(`gubu`)

const shape = Gubu({
  a: Required({x: 1})  // Property `a` is required and must match `{x: 1}`.
})

The Closed builder prohibits an object from having additional unspecified properties:

const { Gubu, Closed } = require(`gubu`)

// Only properties `a` and `b` are allowed.
const shape = Gubu(Closed({
  a: 1,
  b: true
}))

You can also access builders as properties of the main Gubu function, and you can also chain most builders. Thus a Required and Closed object can be specified with:

const { Gubu } = require(`gubu`)

const shape = Gubu({
  a: Gubu.Closed({ x: 1 }).Required(),
  b: Gubu.Required({ x: 1 }).Closed(),  // Also works.
})

You can also write your own builders - see the API Builders section.

In addition to this README, the unit tests are comprehensive and provide many usage examples.

API

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Shape

A shape specification can either be at the root of a JSON structure, an array element, or the value of an object property. For a value to pass validation, it is compared to the shape, and must match the constraints of the shape. If the shape has elements or properties, these must also match, and are validated recursively in a depth-first manner ¹.

Required Scalars

The value must be of the indicated type, and must exist.

• String: match any string, but not the empty string ².
• Number: match any number, but not BigInt values.
• Boolean: match any boolean.
• Symbol: match any symbol.
• BigInt: match any BigInt (including the 1n syntax form).
• Date: match an object created with new Date(...)
• RegExp: match an object created with /.../ or new RegExp(...)

Optional Scalars with Defaults

The value must be of the indicated type, and is derived from the given default. If the value does not exist, the default value is inserted.

• foo: match any string, but replace an empty string ³.
• 123: match any number, but not BigInt values.
• true: match any boolean.
• new Symbol('bar'): match any symbol.
• new BigInt(456): match any BigInt (including the 1n syntax form).
• new Date(): match an object created with new Date(...)
• /x/: match an object created with /.../ or new RegExp(...)

Objects

Arrays

Functions

Validations

Custom Validations

Gubu function

Errors

Builders

Edge Cases

Empty Strings

Unfortunately the empty string is not really a subtype of the string type, since it evaluates to false. In the case of HTTP input, missing parameters values are often provided as empty strings, when they are in fact undefined. There are heartfelt arguments on both sides of this issue.

The engineering compromise is based on the priniciple of explicit notice. Since reasonable people have a reasonable disagreement about this behaviour, a mitigation of the issue is to make it explicit. Thus, the Empty(String), or Empty('foo') shapes need to be used if you want to accept empty strngs.

As a shortcut, you can use '' directly for optional strings, and that shape will accept empty strings, and give you an empty string as a default.

Credits

This module is inspired by Joi, which I used for many years. It also draws from the way Vue does property validation.

GUBU

The name comes from a sort of in-joke in Irish politics. It is grotesque, unbelievable, bizarre and unprecedented, that anyone would write yet another validation library for JavaScript, let alone a third one! (See parambulator and norma - but don't use those, Gubu is better!).

Also I like short names.

License

Copyright (c) 2021, Richard Rodger and other contributors. Licensed under MIT.

Footnotes

Footnotes

1. The implementation algorithm is iterative, just a loop that processes values in depth-first order. ↩

2. An empty string is not considered to match the string type. To allow empty strings, use Empty(String). See Empty Strings. ↩

3. An empty string is not considered to match the string type. To allow empty strings, use Empty('some-default'). See Empty Strings. ↩