data-guard

Data validation is frustrating, let‘s fix that.

You can stop your search for a data validation library now. data-guard has you covered. Why should you not write your own data validations and just use data-guard? Well, because data-guard is:

• Small. Designed so that users don’t have to download a huge library just so you can do data validation.
• Flexible. data-guard will work in any context. By default validators will just return a boolean. If you want error messages you can use the special validate method. In addition data-guard has you covered for any function type validation needs.
• Functional. Functional programming is perhaps the easiest pattern to fit into your application. data-guard does not force you to write your code in a functional manner, but data-guard itself is written to be super compassable and useable with any framework in any codebase.

data-guard is not a JSON schema validator and does not plan to be. We want to keep data-guard as small as possible so you don‘t introduce unnecessary technical debt into your application.

For more information on a React propTypes style usage, look at the Guarding function arguments section!

Need more?

See something missing that is a blocker for your use of data-guard, well instead of writing your own data validation library consider opening an issue. This not only means you can use data-guard, but everyone else who uses it both now and in the future can benefit from your feature request. Let‘s stop using a hundred different data validation frameworks and finally just agree on one.

Usage

Validators accept two parameters in a curried fashion, a config, and a value. For example, the array validator:

var t = require('data-guard')
 
t.items(t.string())(['a', 'b', 'c'])

Represents a validator which ensures that all items in an array are strings. Validators also only return a boolean. true if the validation succeeded, false if it failed. For example, see the following:

var t = require('data-guard')
 
console.log(t.string()('hello, world'))       // => true
console.log(t.string()(2))                    // => false
console.log(t.items(t.number())([1, 2, 'c'])) // => false
console.log(t.items(t.number())([4, 5, 6]))   // => true

Chaining validators

Validators may also be chained together:

var t = require('data-guard')
 
console.log(t.string().match(/@/)('hello, world'))     // => false
console.log(t.string().match(/@/)('[e-mail]')) // => true

These design decisions allow for validators to be hyper flexible. If you want a validator, you just call one and you automatically have a function which you may pass around to other functions, and when called it returns a boolean saying if the value is valid. No specific domain knowledge required of your code, just functions and booleans. However, data-guard does have the capability to do more. See the following:

Getting more information about the validation

var t = require('data-guard')
var validate = require('data-guard').validate
 
console.log(validate(t.string().match(/@/), 'hello, world'))

By using the validate function, you opt to pass in only the validator function (instead of calling it directly) and the value you wish to validate. This allows data-guard to get some extra information about the validation and it will now return the object:

{
  success: false,
  details: [{
    path: '/',
    value: 'hello, world',
    errors: ['match']
  }]
}

The object will always have a success boolean, which is just the boolean value the validator would have returned if called correctly. The results array will contain an object for every failed path in the validation. A path is defined as a JSON pointer and is useful for identifying the field in an object or array environment. For example:

var validator = t.shape({
  foo: t.string(),
  bar: t.number()
})
 
var value = {
  foo: 42,
  bar: 'buz'
}
 
validate(validator, value)

Would return:

{
  success: false,
  details: [{
    path: '/',
    value: { ... },
    errors: ['shape']
  }, {
    path: '/foo',
    value: 42,
    errors: ['string']
  }, {
    path: '/bar',
    value: 'buz',
    errors: ['number']
  }]
}

If multiple validators return an error, all of those errors will be represented in the returned object.

By calling validate.strict(...) instead of validate(...), the function will throw an error on the first failed validator.

Guarding function arguments

Because data-guard really likes functional programming, it also provides a decorator function so you can “guard” your own functions. Making them pseudo-type-safe.

var t = require('data-guard')
var guard = require('data-guard').guard
 
function multiply(a, b) {
  return a * b
}
 
var guardedMultiply = guard(t.number(), t.number())(multiply)

Now, if you call guardedMultiply with a value of the wrong type, say a string, it will warn you in the console. If you would rather fail instead of warn on a bad validation use guard.strict(...) instead of guard(...).

The guard function will take any number of parameters. These parameters are expected to be functions which return a boolean. For each validator passed to guard, the argument in the same place in the decorated function will be validated using that validator.

This function was inspired by React’s propTypes.

Validators

The validators bundled with data-guard by default are:

• any: Always returns true.
• boolean: Value is optionally a boolean type.
• number: Value is optionally a number type.
• string: Value is optionally a string type.
• object: Value is optionally an object type.
• array: Value is optionally an array type.
• function: Value is optionally a function type.
• required: Value may not be null or undefined.
• shape: Value must conform to a certain object shape. Must be passed an object parameter.
• items: All items in the value array must conform to the passed validator. May be passed a shape.
• match: Matches a string to a regular expression.
• enum: Value must be exactly one of the values passed in.
• instanceOf: Value must pass an instanceof check with the supplied function.

If there is another low level validator you would like to see, please open an issue or submit a PR!

Credits

If you use and enjoy this module, the best way to show your gratitude is to follow me, @calebmer, on Twitter.