THIS LIBRARY IS STILL IN DEVELOPMENT AND IN ALPHA. THIS IS A GREAT TIME TO GET INVOLVED WITH CONTRIBUTING TO THIS LIBRARY. ALTHOUGH IT WORKS, USE IT AT YOUR OWN RISK.

Golden Validator

The easy peasy validation library!

Validation is not new and generally present as a feature of a larger framework. With that, the objective of this library is to have a standalone validation tool that can be used anywhere Javascript is used. It is heavily inspired by the functional programming paradigm and even supports Typescript.

Installation

If you use yarn

yarn add golden-validator

If you use npm

npm install golden-validator 

Usage

First, start by creating a schema to act as a constraint for your model. Use the createSchema and createRule methods along with the prebuilt validators to establish a schema.

// schema.js
import {
    isString,
    isEmail,
    isBetween,
    hasMaxLengthOf,
    createRule,
    createSchema
} from 'golden-validator';
 
nameRule = createRule({
    required: true,
    validators: [ isString() ]
});
 
emailRule = createRule({
    required: true,
    validators: [ isEmail(), hasMaxLengthOf(5) ]
});
 
ageRule = createRule({
    validator: [ isBetween(18, 60) ]
});
 
export const userSchema = createSchema<User>({
    name: nameRule,
    email: emailRule,
    age: ageRule
});

Afterwards you can validate your model to see if it violates any rule in your schema. The validate method can be used to obtain array of errors corresponding to each key in the model. If a model field has no error, the value is an empty array.

// example1.js
import { validate } from 'golden-validator';
import { userSchema } from './schema.js';
 
const user: User = {
    email: 'john.doe@test',
}
 
validationResult: ValidationResult<User> = validate(user, userSchema);
console.log(validationResult);
 
/*
{
    name: ['value is required'],
    email: ['value is not an email', 'value length is greater than 5'],
    age: []
}
/*

The example above is meant to demonstrate some rules that the library follows to generate error messages:

• If a value is not required and is not present, no error will be reported and an empty array will be returned.
• If a value is required but not present, only the requirement constraint will be generated.
• If a value is present but fails certain validators, an array of corresponding error messages will be returned. If all validators pass, an empty array will be returned.

If you want to validate a nested model structure, you can use a subschema to define your schema rules.

const breedRule = createRule({
    required: false,
    validators: [ hasMinLengthOf(6) ]
});
 
export const petSchema = createSchema<Pet> ({
    breed: breedRule
});
 
 
// you can then use the petSchema as part of your user rule
import { petSchema } from './pet-schema';
 
const ageRule = createRule({
    required: false,
    validators: [ isNumber() ]
});
 
export const userSchema = createSchema<User> ({
    age: ageRule,
    pet: petSchema // ------> you can use a schema here
});
 
const user: User = {
    age: '15',
    pet: {
        breed: 'corgi'
    },
};
 
console.log(validate(user, userSchema));
 
/*
{
    age: ['value is not a number'],
    pet: {
        breed: ['value length is not greater than 6']
    }
}
*/
 

If you are only concerned with a simple answer regarding whether or not the model has met the rules in the schema, you can take advantage of the isValid method. Using this method is advised as it has been optimized to return an answer when the result becomes immediately evident throughout the evaluation.

// example2.js
import { isValid } from 'golden-validator';
import { userSchema } from './schema.js';
 
const user: User = {
    email: 'john.doe@test',
}
 
isUserValid = isValid(user, userSchema);
console.log(isUserValid); // false

Validators

From the perspective of this library, a validator is an object with 2 keys, evaluator and errorMessage. The evaluator is a function that takes in a value and returns a boolean. The errorMessage is a string that represents the error message returned when the value does not pass the evaluator. For example:

const isGreaterThan10Validator = {
    evaluator: (value) => value > 10,
    errorMessage: 'value is not greater than 10'
}

You can then use isGreaterThan10Validator as a member of the schema's validator array. But rather than hard coding the constraint into the evaluator function and error message, it makes more sense to invoke functions that take constraints as arguments and return an evaluator. For example:

const isGreaterThan = (constraint) => {
    evaluator: (value) => value > constraint,
    errorMessage: `value is not greater than ${constraint}`
}

Rather than trying to write all these validators from scratch, this library includes validators that would typically be used in most applications.

Built-in Validator Factories

Validator Factories	Function Signature
hasLengthOf	(number) => Validator
hasMinLengthOf	(number) => Validator
hasMaxLengthOf	(number) => Validator
inEnum	(array) => Validator
isBetween	(number, number) => Validator
isEmail	( ) => Validator
isEqualTo	(any) => Validator
isFalsy	( ) => Validator
isGreaterThan	(number) => Validator
isLessThan	(number) => Validator
isNumber	( ) => Validator
isTruthy	( ) => Validator
matchesPattern	(RegExp) => Validator

Note: If you believe that a fundamental validator factory is missing from the library, please raise an issue and the need of the validator will be assessed by the maintainers. The idea here is to organically expand the list of validator factories based on input from the community.

Custom Usage

It is easy to write your own validators if you believe the required functionality is not part of this library. For example, let's write a custom validator to check whether or not a substring is included in a string.

const hasSubstring: ValidatorFactory = substring => ({
    evaluator: value => value.includes(substring);
    errorMessage: `does not contain ${substring}`;
})
 
// then you can use it in a schema as such
const userSchema = createSchema<User>({
    domain: createRule({
        required: true
        validators: [
            hasSubstring('http://'),
            ...
        ]
    }):
 
})

You can then use the custom validator and include it in the validators array as seen in the example above. To decouple and easily test your code further, you can use a utility function to create your validators.

import { createValidatorFactory } from 'golden-validator';
 
const createHasSubstringEvaluator = substring => value => value.includes(substring);
const hasSubstringErrorMessage = substring => `value does not contain ${substring}`;
 
const hasSubstring = createValidatorFactory(
  createHasSubstringEvaluator,
  hasSubstringErrorMessage
);