yup

What is yup?

The yup npm package is a JavaScript schema builder for value parsing and validation. It enables developers to construct schemas for objects, arrays, strings, numbers, booleans, and more, to validate the shape and content of data against those schemas. It is often used in the context of form validation on both the client and server sides.

What are yup's main functionalities?

Object Shape Validation

Validates the shape of an object, ensuring that it has specific fields with data types and constraints like strings being required, numbers being positive integers, and strings matching email or URL patterns.

{"const schema = yup.object().shape({ name: yup.string().required(), age: yup.number().required().positive().integer(), email: yup.string().email(), website: yup.string().url() }); schema.isValid({ name: 'John', age: 24, email: '[e-mail]', website: 'http://example.com' }).then(valid => { console.log(valid); // true });"}

Array Validation

Validates arrays, ensuring that they contain elements of a specific type and adhere to constraints, such as all elements being positive numbers.

{"const schema = yup.array().of(yup.number().positive()).required(); schema.isValid([1, 2, 3]).then(valid => { console.log(valid); // true });"}

String Validation

Validates strings, ensuring they meet criteria such as being required, having a minimum length, and not exceeding a maximum length.

{"const schema = yup.string().required().min(2).max(10); schema.isValid('Hello').then(valid => { console.log(valid); // true });"}

Number Validation

Validates numbers, ensuring they are positive, integers, and below a certain value.

{"const schema = yup.number().positive().integer().lessThan(100); schema.isValid(50).then(valid => { console.log(valid); // true });"}

Date Validation

Validates dates, ensuring they fall within a specified range.

{"const schema = yup.date().min(new Date(2000, 0, 1)).max(new Date(2020, 12, 31)); schema.isValid(new Date(2010, 6, 15)).then(valid => { console.log(valid); // true });"}

Custom Validation

Allows for custom validation functions to be defined, providing flexibility for more complex validation scenarios.

{"const schema = yup.string().test('is-john', 'The name must be John', value => value === 'John'); schema.isValid('John').then(valid => { console.log(valid); // true });"}

Other packages similar to yup

joi

Joi is a powerful schema description language and data validator for JavaScript. It offers a similar API to yup but with a broader feature set and more detailed error messages. Joi is often considered more heavyweight compared to yup.

ajv

Ajv is a JSON schema validator that supports draft-06/07/2019-09 of JSON Schema. It is known for its performance and is typically used for validating JSON data structures. Unlike yup, Ajv is based on pre-defined JSON schemas rather than a programmatic API.

validator

Validator is a library of string validators and sanitizers. It is more focused on string validation and does not provide object schema validation like yup. It's useful for simple validation tasks without the need for defining complex schemas.

class-validator

Class-validator works with TypeScript and uses decorators to define validation rules within class models. It is tightly integrated with TypeScript and is a good choice for projects that are already using TypeScript and decorators.

README

Yup

a js object schema validation. The api and style is heavily inspired by Joi, which is an amazing library but generally too big and feature rich for my client use. Yup is a lean lib in the same spirit without the fancy features. You can use it on the server as well, but in that case you might as well just use Joi.

Yup is also a little less opinionated than joi, allowing for custom validation and transformations. It also allows "stacking" conditions via when for properties taht depend on more than one other sibling property.

Usage

You define and create schema objects. Schema objects are immutable, so each call of a method returns a new schema object.

var yup = require('yup')

var schema = yup.object().shape({
  name:      yup.string().required(),
  age:       yup.number().required().positive().integer(),
  email:     yup.string().email(),
  website    yup.string().url(),
  createdOn: yup.date().default(function() { 
    return new Date 
  }),
})

//check validity
schema.isValid({
  name: 'jimmy',
  age: 24
})  
// => true

//you can try and type cast objects to the defined schema
schema.cast({
  name: 'jimmy',
  age: '24',
  createdOn: '2014-09-23T19:25:25Z'
})
// => { name: 'jimmy', age: 24, createdOn: Date }

mixed

Creates a schema that matches all types. All types inherit from this base type

var schema = yup.mixed();
schema.isValid() //=> true

mixed.clone()

Creates a new instance of the schema. Clone is used internally to return a new schema with every schema state change.

mixed.concat(schema)

Creates a new instance of the schema by combining two schemas.

mixed.isValid(value, options)

Returns true when the passed in value matches the schema. if false then the schema also has a .errors field which is an array of validation error messages (strings), thrown by the schema.

The options argument is an object hash containing any schema options you may want to override (or specify for the first time).

• strict -> boolean: default false
• context -> an object hash containing any context for validating schema conditions (see: when())

mixed.cast(value)

Attempts to coerce the passed in value to a value that matches the schema. For example: '5' will cast to 5 when using the number() type. Failed casts generally return null, but may also return results like NaN and unexpected strings.

mixed.isType(value)

Runs a type check against the passed in value. It returns true if it matches, it does not cast the value. When nullable() is set null is considered a valid value of the type.

mixed.strict() (default: false)

Sets the strict option to true, telling the schema to not try and cast the passed in value before validating it.

mixed.default(value)

Sets a default value to use when the value is missing. The value argument can also be a function that returns a default value (useful for setting defaults of by reference types like arrays or objects).

mixed.nullable(isNullable) (default: false)

Indicates that null is a valid value for the schema. Without nullable() null is treated as an empty value and will fail isType() checks.

mixed.required(msg)

Mark the schema as required. All field values asside from undefined meet this requirement.

mixed.oneOf(arrayOfValues)

Whitelist a set of values. Values added are automatically removed from any blacklist if they are in it.

var schema = yup.mixed().oneOf(['jimmy', 42]);
schema.isValid(42)       //=> true
schema.isValid('jimmy')  //=> true
schema.isValid(new Date) //=> false

mixed.notOneOf(arrayOfValues)

Blacklist a set of values. Values added are automatically removed from any whitelist if they are in it.

var schema = yup.mixed().notOneOf(['jimmy', 42]);
schema.isValid(42)       //=> false
schema.isValid(new Date) //=> true

mixed.when(key, options | function)

Adjust the schema based on a sibling or sibling children fields. You can provide an object literal where the key is is a yup schema type, then provides the true schema and/or otherwise for the failure condition. Alternatively you can provide a function the returns a schema ( the this value is the current schema). when conditions are additive.

var inst = yup.object({
      isBig: yup.boolean(), 
      other: yup.number(),
      count: yup.number()
        .when('isBig', { 
          is: true, 
          then:      yup.number().min(5), 
          otherwise: yup.number().min(0) 
        })
        .when('other', function(v){ 
          if (v === 4) return this.max(6)
        })
    })

mixed.validation(message, fn)

Adds a validation function to the validation chain. Validations are run after any object is cast. Many types have some validations built in, but you can create custom ones easily.

for the message argument you can provide a string which is will interpolate certain keys if specified, all validations are given a path value which indicates location.

var schema = yup.mixed().validation('${path} is invalid!', function(value){
  return value !== 'jimmy'
});
schema.isValid('jimmy') //=> true

schema.isValid('john') //=> false
schema.errors // => [ 'this is invalid!']

mixed.transform(fn)

Adds a transformation to the transform chain. Transformations are part of the casting process and run after the value is coerced to the type, but before validations. Transformations will not be applied unless strict is true. Some types have built in transformations.

Transformations are useful for arbitrarily altering how the object is cast. You should take care not to mutate the passed in value if possible.

var schema = yup.string().transform(function(value){
  return value.toUpperCase()
});
schema.cast('jimmy') //=> 'JIMMY'

Static Methods

• Mixed.create(props) - creates a new instance of a type with the specified props
• Mixed.extend(protoProps) - Backbone-esque object inheritance. extend returns a new constructor function that inherits from the type. All types inherit mixed in this manner. Be sure to include a constructor property it is not automatically created.

string

Define a string schema. note: strings are nullable by default.

var schema = yup.string();
schema.isValid('hello') //=> true

string.min(limit, message)

Set an yupmum length limit for the string value. The ${min} interpolation can be used in the message argument

string.max(limit, message)

Set an maximum length limit for the string value. The ${max} interpolation can be used in the message argument

string.matches(regex, message)

Provide an arbitrary regex to match the value against.

var v = string().matches(/(hi|bye)/);
v.isValid('hi').should.equal(true)
v.isValid('nope').should.equal(false)

string.email(message)

Validates the value as an email address via a regex.

string.url(message)

Validates the value as a valid URL via a regex.

string.trim(msg)

Transforms string values by removing leading and trailing whitespace. If strict() is set it will only validate that the value is trimmed.

string.lowercase(msg)

Transforms the string value to lowercase. If strict() is set it will only validate that the value is lowercase.

string.uppercase(msg)

Transforms the string value to uppercase. If strict() is set it will only validate that the value is uppercase.

number

Define a number schema.

var schema = yup.number();
schema.isValid(10) //=> true

number.min(limit, message)

Set the yupmum value allowed. The ${min} interpolation can be used in the message argument.

number.max(limit, message)

Set the maximum value allowed. The ${max} interpolation can be used in the message argument.

number.positive(message)

Value must be a positive number.

number.negative(message)

Value mut be a negative number.

number.integer(message)

Transformation that coerces the value into an integer via truncation value | 0. If strict() is set it will only validate that the value is an integer.

round(type) - 'floor', 'ceil', 'round'

Rounds the value by the specified method (defaults to 'round').

boolean

Define a boolean schema.

var schema = yup.boolean();
schema.isValid(true) //=> true

date

Define a Date schema. By default ISO date strings will parse correctly.

var schema = yup.date();
schema.isValid(new Date) //=> true

date.min(limit, message)

Set the yupmum date allowed.

date.max(limit, message)

Set the maximum date allowed.

array

Define an array schema. Arrays can be typed or not, When specifying the element type, cast and isValid will apply to the elements as well. Options passed into isValid are passed also passed to child schemas.

var schema = yup.array().of(number().min(2));
schema.isValid([2, 3])   //=> true
schema.isValid([1, -24]) //=> false

schema.cast(['2', '3'])  //=> [2, 3] 

array.of(type)

Specify the schema of array elements. It can be any schemaType, and is not required.

array.min(limit, message)

Set an yupmum length limit for the array. The ${min} interpolation can be used in the message argument.

array.max(limit, message)

Set an maximum length limit for the array. The ${max} interpolation can be used in the message argument.

array.compact(rejector)

Removes falsey values from the array. Providing a rejector function lets you specify the rejection criteria yourself.

array()
  .compact()
  .cast(['', 1, 0, 4, false, null]) // => [1,4]

array()
  .compact(function(v){ 
    return v == null 
  })
  .cast(['', 1, 0, 4, false, null]) // => ['',1, 0, 4, false]

object

Define an object schema. Options passed into isValid are passed also passed to child schemas.

yup.object().shape({
  name:      string().required(),
  age:       number().required().positive().integer(),
  email:     string().email(),
  website    string().url(),
}) 

object.shape(schemaHash)

Define the keys of the object and the schemas for said keys.

object.from(fromKey, toKey, alias)

Transforms the specified key to a new key. If alias is true then the old key will be left.

var schema = object()
      .shape({
        myProp: mixed(),
        Other: mixed(),
      })
      .from('prop', 'myProp')
      .from('other', 'Other', true)

inst.cast({ prop: 5, other: 6}) // => { myProp: 5, other: 6, Other: 6 }

object.camelcase()

Transforms all object keys to camelCase

object.constantcase()

Transforms all object keys to CONSTANT_CASE.