@bpinternal/zui
v0.13.0
Published
A fork of Zod with additional features
Downloads
14,566
Maintainers
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Quick start
Installation
pnpm add @bpinternal/zui # pnpm
npm install @bpinternal/zui # npm
yarn add @bpinternal/zui # yarn
bun add @bpinternal/zui # bun
Basic Usage
import { z, UIComponentDefinitions, ZuiComponentMap, ZuiForm } from '@bpinternal/zui'
const schema = z.object({
name: z.string().title('Name').placeholder('John Doe'),
age: z.number().title('Age').placeholder('18'),
})
const serializedSchema = schema.toJsonSchema()
const exampleExtensions = {
string: {
coolInput: {
id: 'coolInput',
params: z.object({
showUnicorns: z.boolean().optional()
}),
},
},
number: {
},
boolean: {
},
array: {
},
object: {
},
discriminatedUnion: {},
} as const satisfies UIComponentDefinitions
import React, { useState } from 'react'
const exampleComponentMap: ZuiComponentMap<typeof exampleExtensions> = {
string: {
coolInput: ({ onChange, errors, required, params, disabled, label, data, zuiProps, schema }) => (
<CoolInput showUnicorns={params.showUnicorns} />
),
default: (props) => null
},
// implement all components here ...
}
const MyForm = () => {
const [formData, setFormData] = useState({})
return (
<>
<ZuiForm<typeof exampleExtensions>
schema={serializedSchema}
value={formData}
onChange={setFormData}
components={exampleComponentMap}
disableValidation={false}
/>
</>
)
}
Documentation
- Quick Start
- Introduction
- Installation
- Basic usage
- Primitives
- Extensions
- Displaying Forms
- Coercion for primitives
- Literals
- Strings
- Numbers
- BigInts
- NaNs
- Booleans
- Dates
- Zod enums
- Native enums
- Optionals
- Nullables
- Objects
- Arrays
- Tuples
- Unions
- Discriminated unions
- Records
- Maps
- Sets
- Intersections
- Recursive types
- Promises
- Instanceof
- Functions
- Template Literals
- Preprocess
- Custom schemas
- Schema methods
- Guides and concepts
Introduction
Zod is a TypeScript-first schema declaration and validation library. I'm using the term "schema" to broadly refer to any data type, from a simple string
to a complex nested object.
Zod is designed to be as developer-friendly as possible. The goal is to eliminate duplicative type declarations. With Zod, you declare a validator once and Zod will automatically infer the static TypeScript type. It's easy to compose simpler types into complex data structures.
Some other great aspects:
- Zero dependencies
- Works in Node.js and all modern browsers
- Tiny: 8kb minified + zipped
- Immutable: methods (e.g.
.optional()
) return a new instance - Concise, chainable interface
- Functional approach: parse, don't validate
- Works with plain JavaScript too! You don't need to use TypeScript.
Installation
Requirements
TypeScript 4.5+!
You must enable
strict
mode in yourtsconfig.json
. This is a best practice for all TypeScript projects.// tsconfig.json { // ... "compilerOptions": { // ... "strict": true } }
From npm
(Node/Bun)
npm install @bpinternal/zui # npm
yarn add @bpinternal/zui # yarn
bun add @bpinternal/zui # bun
pnpm add @bpinternal/zui # pnpm
Basic usage
Creating a simple string schema
import { z } from '@bpinternal/zui'
// creating a schema for strings
const mySchema = z.string()
// parsing
mySchema.parse('tuna') // => "tuna"
mySchema.parse(12) // => throws ZodError
// "safe" parsing (doesn't throw error if validation fails)
mySchema.safeParse('tuna') // => { success: true; data: "tuna" }
mySchema.safeParse(12) // => { success: false; error: ZodError }
Creating an object schema
import { z } from '@bpinternal/zui'
const User = z.object({
username: z.string(),
})
User.parse({ username: 'Ludwig' })
// extract the inferred type
type User = z.infer<typeof User>
// { username: string }
Primitives
import { z } from '@bpinternal/zui'
// primitive values
z.string()
z.number()
z.bigint()
z.boolean()
z.date()
z.symbol()
// empty types
z.undefined()
z.null()
z.void() // accepts undefined
// catch-all types
// allows any value
z.any()
z.unknown()
// never type
// allows no values
z.never()
Extensions
Zui extends Zod by adding additional methods for customizing the UI of your schema
.title(text: string)
Saves the title to display in the UI, if not specified, a title will be generated from the key
.placeholder(text: string)
Saves the placeholder to display in the UI's field, if not specified, no placeholder will be displayed.
.displayAs<ComponentDefinition>({ id: string, params: object })
Specifies the component to use for displaying the field, if not specified, the default component will be used.
The type of params
comes from the component definition.
.hidden(condition?: boolean | (currentValue) => boolean | object)
Hides/shows the component, the condition is optional, if .hidden()
is called without a condition, the component will be hidden by default.
It can also be a function that receives the current value of the field and returns a boolean.
In the case of objects and arrays, a partial object can be passed to hide/show specific fields.
example:
z.object({
name: z.string()
age: z.number()
}).hidden(formData => {
return {
age: formData.name?.length < 1 // the age field will be hidden if the name field is empty
}
})
.disabled(condition?: boolean | (currentValue) => boolean)
Disables/enables the component, the condition is optional, if .disabled()
is called without a condition, the component will be disabled by default.
It can also be a function that receives the current value of the field and returns a boolean.
In the case of objects and arrays, a partial object can be passed to hide/show specific fields.
example:
z.object({
name: z.string()
age: z.number()
}).hidden(formData => {
return {
age: formData.name?.length < 1 // the age field will be hidden if the name field is empty
}
})
.toJsonSchema(options?: ToJsonSchemaOptions)
Converts the schema to a JSON schema, by default it targets 'openApi3'
options can be passed to customize the output:
{
target: "openApi3" | "jsonSchema7" | undefined, // defaults to openApi3
$schemaUrl: string | false | undefined // if not false, will default to the appropriate schema url for the target
unionStrategy: "oneOf" | "anyOf" | undefined // defaults to anyOf
}
.toTypescript()
.toTypescriptAsync()
Zod.fromJsonSchema()
Zod.fromObject()
Displaying Forms
TODO
Coercion for primitives
Zod now provides a more convenient way to coerce primitive values.
const schema = z.coerce.string()
schema.parse('tuna') // => "tuna"
schema.parse(12) // => "12"
During the parsing step, the input is passed through the String()
function, which is a JavaScript built-in for coercing data into strings.
The returned schema is a normal ZodString
instance so you can use all string methods.
z.coerce.string().email().min(5)
How coercion works
All primitive types support coercion. Zod coerces all inputs using the built-in constructors: String(input)
, Number(input)
, new Date(input)
, etc.
z.coerce.string() // String(input)
z.coerce.number() // Number(input)
z.coerce.boolean() // Boolean(input)
z.coerce.bigint() // BigInt(input)
z.coerce.date() // new Date(input)
Note that some behavior may not be what you expect.
schema.parse(true) // => "true"
schema.parse(undefined) // => "undefined"
schema.parse(null) // => "null"
For more control over coercion logic, consider using z.preprocess
or z.pipe()
.
Boolean coercion
Zod's approach to coercion is very simple! It passes the value into the Boolean(value)
function, that's it. Any truthy value will resolve to true
, any falsy value will resolve to false
.
z.coerce.boolean().parse('tuna') // => true
z.coerce.boolean().parse('true') // => true
z.coerce.boolean().parse('false') // => true
z.coerce.boolean().parse(1) // => true
z.coerce.boolean().parse([]) // => true
z.coerce.boolean().parse(0) // => false
z.coerce.boolean().parse('') // => false
z.coerce.boolean().parse(undefined) // => false
z.coerce.boolean().parse(null) // => false
Literals
Literal schemas represent a literal type, like "hello world"
or 5
.
const tuna = z.literal('tuna')
const twelve = z.literal(12)
const twobig = z.literal(2n) // bigint literal
const tru = z.literal(true)
const terrificSymbol = Symbol('terrific')
const terrific = z.literal(terrificSymbol)
// retrieve literal value
tuna.value // "tuna"
Currently there is no support for Date literals in Zod. If you have a use case for this feature, please file an issue.
Strings
Zod includes a handful of string-specific validations.
// validations
z.string().max(5)
z.string().min(5)
z.string().length(5)
z.string().email()
z.string().url()
z.string().emoji()
z.string().uuid()
z.string().cuid()
z.string().cuid2()
z.string().ulid()
z.string().regex(regex)
z.string().includes(string)
z.string().startsWith(string)
z.string().endsWith(string)
z.string().datetime() // ISO 8601; default is without UTC offset, see below for options
z.string().ip() // defaults to IPv4 and IPv6, see below for options
// transformations
z.string().trim() // trim whitespace
z.string().toLowerCase() // toLowerCase
z.string().toUpperCase() // toUpperCase
Check out validator.js for a bunch of other useful string validation functions that can be used in conjunction with Refinements.
You can customize some common error messages when creating a string schema.
const name = z.string({
required_error: 'Name is required',
invalid_type_error: 'Name must be a string',
})
When using validation methods, you can pass in an additional argument to provide a custom error message.
z.string().min(5, { message: 'Must be 5 or more characters long' })
z.string().max(5, { message: 'Must be 5 or fewer characters long' })
z.string().length(5, { message: 'Must be exactly 5 characters long' })
z.string().email({ message: 'Invalid email address' })
z.string().url({ message: 'Invalid url' })
z.string().emoji({ message: 'Contains non-emoji characters' })
z.string().uuid({ message: 'Invalid UUID' })
z.string().includes('tuna', { message: 'Must include tuna' })
z.string().startsWith('https://', { message: 'Must provide secure URL' })
z.string().endsWith('.com', { message: 'Only .com domains allowed' })
z.string().datetime({ message: 'Invalid datetime string! Must be UTC.' })
z.string().ip({ message: 'Invalid IP address' })
ISO datetimes
The z.string().datetime()
method enforces ISO 8601; default is no timezone offsets and arbitrary sub-second decimal precision.
const datetime = z.string().datetime()
datetime.parse('2020-01-01T00:00:00Z') // pass
datetime.parse('2020-01-01T00:00:00.123Z') // pass
datetime.parse('2020-01-01T00:00:00.123456Z') // pass (arbitrary precision)
datetime.parse('2020-01-01T00:00:00+02:00') // fail (no offsets allowed)
Timezone offsets can be allowed by setting the offset
option to true
.
const datetime = z.string().datetime({ offset: true })
datetime.parse('2020-01-01T00:00:00+02:00') // pass
datetime.parse('2020-01-01T00:00:00.123+02:00') // pass (millis optional)
datetime.parse('2020-01-01T00:00:00.123+0200') // pass (millis optional)
datetime.parse('2020-01-01T00:00:00.123+02') // pass (only offset hours)
datetime.parse('2020-01-01T00:00:00Z') // pass (Z still supported)
You can additionally constrain the allowable precision
. By default, arbitrary sub-second precision is supported (but optional).
const datetime = z.string().datetime({ precision: 3 })
datetime.parse('2020-01-01T00:00:00.123Z') // pass
datetime.parse('2020-01-01T00:00:00Z') // fail
datetime.parse('2020-01-01T00:00:00.123456Z') // fail
IP addresses
The z.string().ip()
method by default validate IPv4 and IPv6.
const ip = z.string().ip()
ip.parse('192.168.1.1') // pass
ip.parse('84d5:51a0:9114:1855:4cfa:f2d7:1f12:7003') // pass
ip.parse('84d5:51a0:9114:1855:4cfa:f2d7:1f12:192.168.1.1') // pass
ip.parse('256.1.1.1') // fail
ip.parse('84d5:51a0:9114:gggg:4cfa:f2d7:1f12:7003') // fail
You can additionally set the IP version
.
const ipv4 = z.string().ip({ version: 'v4' })
ipv4.parse('84d5:51a0:9114:1855:4cfa:f2d7:1f12:7003') // fail
const ipv6 = z.string().ip({ version: 'v6' })
ipv6.parse('192.168.1.1') // fail
Numbers
You can customize certain error messages when creating a number schema.
const age = z.number({
required_error: 'Age is required',
invalid_type_error: 'Age must be a number',
})
Zod includes a handful of number-specific validations.
z.number().gt(5)
z.number().gte(5) // alias .min(5)
z.number().lt(5)
z.number().lte(5) // alias .max(5)
z.number().int() // value must be an integer
z.number().positive() // > 0
z.number().nonnegative() // >= 0
z.number().negative() // < 0
z.number().nonpositive() // <= 0
z.number().multipleOf(5) // Evenly divisible by 5. Alias .step(5)
z.number().finite() // value must be finite, not Infinity or -Infinity
z.number().safe() // value must be between Number.MIN_SAFE_INTEGER and Number.MAX_SAFE_INTEGER
Optionally, you can pass in a second argument to provide a custom error message.
z.number().lte(5, { message: 'this👏is👏too👏big' })
BigInts
Zod includes a handful of bigint-specific validations.
z.bigint().gt(5n)
z.bigint().gte(5n) // alias `.min(5n)`
z.bigint().lt(5n)
z.bigint().lte(5n) // alias `.max(5n)`
z.bigint().positive() // > 0n
z.bigint().nonnegative() // >= 0n
z.bigint().negative() // < 0n
z.bigint().nonpositive() // <= 0n
z.bigint().multipleOf(5n) // Evenly divisible by 5n.
NaNs
You can customize certain error messages when creating a nan schema.
const isNaN = z.nan({
required_error: 'isNaN is required',
invalid_type_error: "isNaN must be 'not a number'",
})
Booleans
You can customize certain error messages when creating a boolean schema.
const isActive = z.boolean({
required_error: 'isActive is required',
invalid_type_error: 'isActive must be a boolean',
})
Dates
Use z.date() to validate Date
instances.
z.date().safeParse(new Date()) // success: true
z.date().safeParse('2022-01-12T00:00:00.000Z') // success: false
You can customize certain error messages when creating a date schema.
const myDateSchema = z.date({
required_error: 'Please select a date and time',
invalid_type_error: "That's not a date!",
})
Zod provides a handful of date-specific validations.
z.date().min(new Date('1900-01-01'), { message: 'Too old' })
z.date().max(new Date(), { message: 'Too young!' })
Coercion to Date
Since zod 3.20, use z.coerce.date()
to pass the input through new Date(input)
.
const dateSchema = z.coerce.date()
type DateSchema = z.infer<typeof dateSchema>
// type DateSchema = Date
/* valid dates */
console.log(dateSchema.safeParse('2023-01-10T00:00:00.000Z').success) // true
console.log(dateSchema.safeParse('2023-01-10').success) // true
console.log(dateSchema.safeParse('1/10/23').success) // true
console.log(dateSchema.safeParse(new Date('1/10/23')).success) // true
/* invalid dates */
console.log(dateSchema.safeParse('2023-13-10').success) // false
console.log(dateSchema.safeParse('0000-00-00').success) // false
For older zod versions, use z.preprocess
like described in this thread.
Zod enums
const FishEnum = z.enum(['Salmon', 'Tuna', 'Trout'])
type FishEnum = z.infer<typeof FishEnum>
// 'Salmon' | 'Tuna' | 'Trout'
z.enum
is a Zod-native way to declare a schema with a fixed set of allowable string values. Pass the array of values directly into z.enum()
. Alternatively, use as const
to define your enum values as a tuple of strings. See the const assertion docs for details.
const VALUES = ['Salmon', 'Tuna', 'Trout'] as const
const FishEnum = z.enum(VALUES)
This is not allowed, since Zod isn't able to infer the exact values of each element.
const fish = ['Salmon', 'Tuna', 'Trout']
const FishEnum = z.enum(fish)
.enum
To get autocompletion with a Zod enum, use the .enum
property of your schema:
FishEnum.enum.Salmon // => autocompletes
FishEnum.enum
/*
=> {
Salmon: "Salmon",
Tuna: "Tuna",
Trout: "Trout",
}
*/
You can also retrieve the list of options as a tuple with the .options
property:
FishEnum.options // ["Salmon", "Tuna", "Trout"];
.exclude/.extract()
You can create subsets of a Zod enum with the .exclude
and .extract
methods.
const FishEnum = z.enum(['Salmon', 'Tuna', 'Trout'])
const SalmonAndTrout = FishEnum.extract(['Salmon', 'Trout'])
const TunaOnly = FishEnum.exclude(['Salmon', 'Trout'])
Native enums
Zod enums are the recommended approach to defining and validating enums. But if you need to validate against an enum from a third-party library (or you don't want to rewrite your existing enums) you can use z.nativeEnum()
.
Numeric enums
enum Fruits {
Apple,
Banana,
}
const FruitEnum = z.nativeEnum(Fruits)
type FruitEnum = z.infer<typeof FruitEnum> // Fruits
FruitEnum.parse(Fruits.Apple) // passes
FruitEnum.parse(Fruits.Banana) // passes
FruitEnum.parse(0) // passes
FruitEnum.parse(1) // passes
FruitEnum.parse(3) // fails
String enums
enum Fruits {
Apple = 'apple',
Banana = 'banana',
Cantaloupe, // you can mix numerical and string enums
}
const FruitEnum = z.nativeEnum(Fruits)
type FruitEnum = z.infer<typeof FruitEnum> // Fruits
FruitEnum.parse(Fruits.Apple) // passes
FruitEnum.parse(Fruits.Cantaloupe) // passes
FruitEnum.parse('apple') // passes
FruitEnum.parse('banana') // passes
FruitEnum.parse(0) // passes
FruitEnum.parse('Cantaloupe') // fails
Const enums
The .nativeEnum()
function works for as const
objects as well. ⚠️ as const
requires TypeScript 3.4+!
const Fruits = {
Apple: 'apple',
Banana: 'banana',
Cantaloupe: 3,
} as const
const FruitEnum = z.nativeEnum(Fruits)
type FruitEnum = z.infer<typeof FruitEnum> // "apple" | "banana" | 3
FruitEnum.parse('apple') // passes
FruitEnum.parse('banana') // passes
FruitEnum.parse(3) // passes
FruitEnum.parse('Cantaloupe') // fails
You can access the underlying object with the .enum
property:
FruitEnum.enum.Apple // "apple"
Optionals
You can make any schema optional with z.optional()
. This wraps the schema in a ZodOptional
instance and returns the result.
const schema = z.optional(z.string())
schema.parse(undefined) // => returns undefined
type A = z.infer<typeof schema> // string | undefined
For convenience, you can also call the .optional()
method on an existing schema.
const user = z.object({
username: z.string().optional(),
})
type C = z.infer<typeof user> // { username?: string | undefined };
You can extract the wrapped schema from a ZodOptional
instance with .unwrap()
.
const stringSchema = z.string()
const optionalString = stringSchema.optional()
optionalString.unwrap() === stringSchema // true
Nullables
Similarly, you can create nullable types with z.nullable()
.
const nullableString = z.nullable(z.string())
nullableString.parse('asdf') // => "asdf"
nullableString.parse(null) // => null
Or use the .nullable()
method.
const E = z.string().nullable() // equivalent to nullableString
type E = z.infer<typeof E> // string | null
Extract the inner schema with .unwrap()
.
const stringSchema = z.string()
const nullableString = stringSchema.nullable()
nullableString.unwrap() === stringSchema // true
Objects
// all properties are required by default
const Dog = z.object({
name: z.string(),
age: z.number(),
})
// extract the inferred type like this
type Dog = z.infer<typeof Dog>
// equivalent to:
type Dog = {
name: string
age: number
}
.shape
Use .shape
to access the schemas for a particular key.
Dog.shape.name // => string schema
Dog.shape.age // => number schema
.keyof
Use .keyof
to create a ZodEnum
schema from the keys of an object schema.
const keySchema = Dog.keyof()
keySchema // ZodEnum<["name", "age"]>
.extend
You can add additional fields to an object schema with the .extend
method.
const DogWithBreed = Dog.extend({
breed: z.string(),
})
You can use .extend
to overwrite fields! Be careful with this power!
.merge
Equivalent to A.extend(B.shape)
.
const BaseTeacher = z.object({ students: z.array(z.string()) })
const HasID = z.object({ id: z.string() })
const Teacher = BaseTeacher.merge(HasID)
type Teacher = z.infer<typeof Teacher> // => { students: string[], id: string }
If the two schemas share keys, the properties of B overrides the property of A. The returned schema also inherits the "unknownKeys" policy (strip/strict/passthrough) and the catchall schema of B.
.pick/.omit
Inspired by TypeScript's built-in Pick
and Omit
utility types, all Zod object schemas have .pick
and .omit
methods that return a modified version. Consider this Recipe schema:
const Recipe = z.object({
id: z.string(),
name: z.string(),
ingredients: z.array(z.string()),
})
To only keep certain keys, use .pick
.
const JustTheName = Recipe.pick({ name: true })
type JustTheName = z.infer<typeof JustTheName>
// => { name: string }
To remove certain keys, use .omit
.
const NoIDRecipe = Recipe.omit({ id: true })
type NoIDRecipe = z.infer<typeof NoIDRecipe>
// => { name: string, ingredients: string[] }
.partial
Inspired by the built-in TypeScript utility type Partial, the .partial
method makes all properties optional.
Starting from this object:
const user = z.object({
email: z.string(),
username: z.string(),
})
// { email: string; username: string }
We can create a partial version:
const partialUser = user.partial()
// { email?: string | undefined; username?: string | undefined }
You can also specify which properties to make optional:
const optionalEmail = user.partial({
email: true,
})
/*
{
email?: string | undefined;
username: string
}
*/
.deepPartial
The .partial
method is shallow — it only applies one level deep. There is also a "deep" version:
const user = z.object({
username: z.string(),
location: z.object({
latitude: z.number(),
longitude: z.number(),
}),
strings: z.array(z.object({ value: z.string() })),
})
const deepPartialUser = user.deepPartial()
/*
{
username?: string | undefined,
location?: {
latitude?: number | undefined;
longitude?: number | undefined;
} | undefined,
strings?: { value?: string}[]
}
*/
Important limitation: deep partials only work as expected in hierarchies of objects, arrays, and tuples.
.required
Contrary to the .partial
method, the .required
method makes all properties required.
Starting from this object:
const user = z
.object({
email: z.string(),
username: z.string(),
})
.partial()
// { email?: string | undefined; username?: string | undefined }
We can create a required version:
const requiredUser = user.required()
// { email: string; username: string }
You can also specify which properties to make required:
const requiredEmail = user.required({
email: true,
})
/*
{
email: string;
username?: string | undefined;
}
*/
.passthrough
By default Zod object schemas strip out unrecognized keys during parsing.
const person = z.object({
name: z.string(),
})
person.parse({
name: 'bob dylan',
extraKey: 61,
})
// => { name: "bob dylan" }
// extraKey has been stripped
Instead, if you want to pass through unknown keys, use .passthrough()
.
person.passthrough().parse({
name: 'bob dylan',
extraKey: 61,
})
// => { name: "bob dylan", extraKey: 61 }
.strict
By default Zod object schemas strip out unrecognized keys during parsing. You can disallow unknown keys with .strict()
. If there are any unknown keys in the input, Zod will throw an error.
const person = z
.object({
name: z.string(),
})
.strict()
person.parse({
name: 'bob dylan',
extraKey: 61,
})
// => throws ZodError
.strip
You can use the .strip
method to reset an object schema to the default behavior (stripping unrecognized keys).
.catchall
You can pass a "catchall" schema into an object schema. All unknown keys will be validated against it.
const person = z
.object({
name: z.string(),
})
.catchall(z.number())
person.parse({
name: 'bob dylan',
validExtraKey: 61, // works fine
})
person.parse({
name: 'bob dylan',
validExtraKey: false, // fails
})
// => throws ZodError
Using .catchall()
obviates .passthrough()
, .strip()
, or .strict()
. All keys are now considered "known".
Arrays
const stringArray = z.array(z.string())
// equivalent
const stringArray = z.string().array()
Be careful with the .array()
method. It returns a new ZodArray
instance. This means the order in which you call methods matters. For instance:
z.string().optional().array() // (string | undefined)[]
z.string().array().optional() // string[] | undefined
.element
Use .element
to access the schema for an element of the array.
stringArray.element // => string schema
.nonempty
If you want to ensure that an array contains at least one element, use .nonempty()
.
const nonEmptyStrings = z.string().array().nonempty()
// the inferred type is now
// [string, ...string[]]
nonEmptyStrings.parse([]) // throws: "Array cannot be empty"
nonEmptyStrings.parse(['Ariana Grande']) // passes
You can optionally specify a custom error message:
// optional custom error message
const nonEmptyStrings = z.string().array().nonempty({
message: "Can't be empty!",
})
.min/.max/.length
z.string().array().min(5) // must contain 5 or more items
z.string().array().max(5) // must contain 5 or fewer items
z.string().array().length(5) // must contain 5 items exactly
Unlike .nonempty()
these methods do not change the inferred type.
Tuples
Unlike arrays, tuples have a fixed number of elements and each element can have a different type.
const athleteSchema = z.tuple([
z.string(), // name
z.number(), // jersey number
z.object({
pointsScored: z.number(),
}), // statistics
])
type Athlete = z.infer<typeof athleteSchema>
// type Athlete = [string, number, { pointsScored: number }]
A variadic ("rest") argument can be added with the .rest
method.
const variadicTuple = z.tuple([z.string()]).rest(z.number())
const result = variadicTuple.parse(['hello', 1, 2, 3])
// => [string, ...number[]];
Unions
Zod includes a built-in z.union
method for composing "OR" types.
const stringOrNumber = z.union([z.string(), z.number()])
stringOrNumber.parse('foo') // passes
stringOrNumber.parse(14) // passes
Zod will test the input against each of the "options" in order and return the first value that validates successfully.
For convenience, you can also use the .or
method:
const stringOrNumber = z.string().or(z.number())
Optional string validation:
To validate an optional form input, you can union the desired string validation with an empty string literal.
This example validates an input that is optional but needs to contain a valid URL:
const optionalUrl = z.union([z.string().url().nullish(), z.literal('')])
console.log(optionalUrl.safeParse(undefined).success) // true
console.log(optionalUrl.safeParse(null).success) // true
console.log(optionalUrl.safeParse('').success) // true
console.log(optionalUrl.safeParse('https://zod.dev').success) // true
console.log(optionalUrl.safeParse('not a valid url').success) // false
Discriminated unions
A discriminated union is a union of object schemas that all share a particular key.
type MyUnion = { status: 'success'; data: string } | { status: 'failed'; error: Error }
Such unions can be represented with the z.discriminatedUnion
method. This enables faster evaluation, because Zod can check the discriminator key (status
in the example above) to determine which schema should be used to parse the input. This makes parsing more efficient and lets Zod report friendlier errors.
With the basic union method, the input is tested against each of the provided "options", and in the case of invalidity, issues for all the "options" are shown in the zod error. On the other hand, the discriminated union allows for selecting just one of the "options", testing against it, and showing only the issues related to this "option".
const myUnion = z.discriminatedUnion('status', [
z.object({ status: z.literal('success'), data: z.string() }),
z.object({ status: z.literal('failed'), error: z.instanceof(Error) }),
])
myUnion.parse({ status: 'success', data: 'yippie ki yay' })
You can extract a reference to the array of schemas with the .options
property.
myUnion.options // [ZodObject<...>, ZodObject<...>]
To merge two or more discriminated unions, use .options
with destructuring.
const A = z.discriminatedUnion('status', [
/* options */
])
const B = z.discriminatedUnion('status', [
/* options */
])
const AB = z.discriminatedUnion('status', [...A.options, ...B.options])
Records
Record schemas are used to validate types such as Record<string, number>
. This is particularly useful for storing or caching items by ID.
const User = z.object({ name: z.string() })
const UserStore = z.record(z.string(), User)
type UserStore = z.infer<typeof UserStore>
// => Record<string, { name: string }>
The schema and inferred type can be used like so:
const userStore: UserStore = {}
userStore['77d2586b-9e8e-4ecf-8b21-ea7e0530eadd'] = {
name: 'Carlotta',
} // passes
userStore['77d2586b-9e8e-4ecf-8b21-ea7e0530eadd'] = {
whatever: 'Ice cream sundae',
} // TypeError
A note on numerical keys
While z.record(keyType, valueType)
is able to accept numerical key types and TypeScript's built-in Record type is Record<KeyType, ValueType>
, it's hard to represent the TypeScript type Record<number, any>
in Zod.
As it turns out, TypeScript's behavior surrounding [k: number]
is a little unintuitive:
const testMap: { [k: number]: string } = {
1: 'one',
}
for (const key in testMap) {
console.log(`${key}: ${typeof key}`)
}
// prints: `1: string`
As you can see, JavaScript automatically casts all object keys to strings under the hood. Since Zod is trying to bridge the gap between static and runtime types, it doesn't make sense to provide a way of creating a record schema with numerical keys, since there's no such thing as a numerical key in runtime JavaScript.
Maps
const stringNumberMap = z.map(z.string(), z.number())
type StringNumberMap = z.infer<typeof stringNumberMap>
// type StringNumberMap = Map<string, number>
Sets
const numberSet = z.set(z.number())
type NumberSet = z.infer<typeof numberSet>
// type NumberSet = Set<number>
Set schemas can be further constrained with the following utility methods.
z.set(z.string()).nonempty() // must contain at least one item
z.set(z.string()).min(5) // must contain 5 or more items
z.set(z.string()).max(5) // must contain 5 or fewer items
z.set(z.string()).size(5) // must contain 5 items exactly
Intersections
Intersections are useful for creating "logical AND" types. This is useful for intersecting two object types.
const Person = z.object({
name: z.string(),
})
const Employee = z.object({
role: z.string(),
})
const EmployedPerson = z.intersection(Person, Employee)
// equivalent to:
const EmployedPerson = Person.and(Employee)
Though in many cases, it is recommended to use A.merge(B)
to merge two objects. The .merge
method returns a new ZodObject
instance, whereas A.and(B)
returns a less useful ZodIntersection
instance that lacks common object methods like pick
and omit
.
const a = z.union([z.number(), z.string()])
const b = z.union([z.number(), z.boolean()])
const c = z.intersection(a, b)
type c = z.infer<typeof c> // => number
Recursive types
You can define a recursive schema in Zod, but because of a limitation of TypeScript, their type can't be statically inferred. Instead you'll need to define the type definition manually, and provide it to Zod as a "type hint".
const baseCategorySchema = z.object({
name: z.string(),
})
type Category = z.infer<typeof baseCategorySchema> & {
subcategories: Category[]
}
const categorySchema: z.ZodType<Category> = baseCategorySchema.extend({
subcategories: z.lazy(() => categorySchema.array()),
})
categorySchema.parse({
name: 'People',
subcategories: [
{
name: 'Politicians',
subcategories: [
{
name: 'Presidents',
subcategories: [],
},
],
},
],
}) // passes
Thanks to crasite for this example.
ZodType with ZodEffects
When using z.ZodType
with z.ZodEffects
(
.refine
,
.transform
,
preprocess
,
etc...
), you will need to define the input and output types of the schema. z.ZodType<Output, z.ZodTypeDef, Input>
const isValidId = (id: string): id is `${string}/${string}` => id.split('/').length === 2
const baseSchema = z.object({
id: z.string().refine(isValidId),
})
type Input = z.input<typeof baseSchema> & {
children: Input[]
}
type Output = z.output<typeof baseSchema> & {
children: Output[]
}
const schema: z.ZodType<Output, z.ZodTypeDef, Input> = baseSchema.extend({
children: z.lazy(() => schema.array()),
})
Thanks to marcus13371337 and JoelBeeldi for this example.
JSON type
If you want to validate any JSON value, you can use the snippet below.
const literalSchema = z.union([z.string(), z.number(), z.boolean(), z.null()])
type Literal = z.infer<typeof literalSchema>
type Json = Literal | { [key: string]: Json } | Json[]
const jsonSchema: z.ZodType<Json> = z.lazy(() => z.union([literalSchema, z.array(jsonSchema), z.record(jsonSchema)]))
jsonSchema.parse(data)
Thanks to ggoodman for suggesting this.
Cyclical objects
Despite supporting recursive schemas, passing cyclical data into Zod will cause an infinite loop.
Promises
const numberPromise = z.promise(z.number())
"Parsing" works a little differently with promise schemas. Validation happens in two parts:
- Zod synchronously checks that the input is an instance of Promise (i.e. an object with
.then
and.catch
methods.). - Zod uses
.then
to attach an additional validation step onto the existing Promise. You'll have to use.catch
on the returned Promise to handle validation failures.
numberPromise.parse('tuna')
// ZodError: Non-Promise type: string
numberPromise.parse(Promise.resolve('tuna'))
// => Promise<number>
const test = async () => {
await numberPromise.parse(Promise.resolve('tuna'))
// ZodError: Non-number type: string
await numberPromise.parse(Promise.resolve(3.14))
// => 3.14
}
Instanceof
You can use z.instanceof
to check that the input is an instance of a class. This is useful to validate inputs against classes that are exported from third-party libraries.
class Test {
name: string
}
const TestSchema = z.instanceof(Test)
const blob: any = 'whatever'
TestSchema.parse(new Test()) // passes
TestSchema.parse(blob) // throws
Functions
Zod also lets you define "function schemas". This makes it easy to validate the inputs and outputs of a function without intermixing your validation code and "business logic".
You can create a function schema with z.function(args, returnType)
.
const myFunction = z.function()
type myFunction = z.infer<typeof myFunction>
// => ()=>unknown
Define inputs and outputs.
const myFunction = z
.function()
.args(z.string(), z.number()) // accepts an arbitrary number of arguments
.returns(z.boolean())
type myFunction = z.infer<typeof myFunction>
// => (arg0: string, arg1: number)=>boolean
Function schemas have an .implement()
method which accepts a function and returns a new function that automatically validates its inputs and outputs.
const trimmedLength = z
.function()
.args(z.string()) // accepts an arbitrary number of arguments
.returns(z.number())
.implement((x) => {
// TypeScript knows x is a string!
return x.trim().length
})
trimmedLength('sandwich') // => 8
trimmedLength(' asdf ') // => 4
If you only care about validating inputs, just don't call the .returns()
method. The output type will be inferred from the implementation.
You can use the special
z.void()
option if your function doesn't return anything. This will let Zod properly infer the type of void-returning functions. (Void-returning functions actually return undefined.)
const myFunction = z
.function()
.args(z.string())
.implement((arg) => {
return [arg.length]
})
myFunction // (arg: string)=>number[]
Extract the input and output schemas from a function schema.
myFunction.parameters()
// => ZodTuple<[ZodString, ZodNumber]>
myFunction.returnType()
// => ZodBoolean
Preprocess
Zod now supports primitive coercion without the need for
.preprocess()
. See the coercion docs for more information.
Typically Zod operates under a "parse then transform" paradigm. Zod validates the input first, then passes it through a chain of transformation functions. (For more information about transforms, read the .transform docs.)
But sometimes you want to apply some transform to the input before parsing happens. A common use case: type coercion. Zod enables this with the z.preprocess()
.
const castToString = z.preprocess((val) => String(val), z.string())
This returns a ZodEffects
instance. ZodEffects
is a wrapper class that contains all logic pertaining to preprocessing, refinements, and transforms.
Custom schemas
You can create a Zod schema for any TypeScript type by using z.custom()
. This is useful for creating schemas for types that are not supported by Zod out of the box, such as template string literals.
const px = z.custom<`${number}px`>((val) => {
return typeof val === 'string' ? /^\d+px$/.test(val) : false
})
type px = z.infer<typeof px> // `${number}px`
px.parse('42px') // "42px"
px.parse('42vw') // throws;
If you don't provide a validation function, Zod will allow any value. This can be dangerous!
z.custom<{ arg: string }>() // performs no validation
You can customize the error message and other options by passing a second argument. This parameter works the same way as the params parameter of .refine
.
z.custom<...>((val) => ..., "custom error message");
Schema methods
All Zod schemas contain certain methods.
.parse
.parse(data: unknown): T
Given any Zod schema, you can call its .parse
method to check data
is valid. If it is, a value is returned with full type information! Otherwise, an error is thrown.
IMPORTANT: The value returned by
.parse
is a deep clone of the variable you passed in.
const stringSchema = z.string()
stringSchema.parse('fish') // => returns "fish"
stringSchema.parse(12) // throws error
.parseAsync
.parseAsync(data:unknown): Promise<T>
If you use asynchronous refinements or transforms (more on those later), you'll need to use .parseAsync
.
const stringSchema = z.string().refine(async (val) => val.length <= 8)
await stringSchema.parseAsync('hello') // => returns "hello"
await stringSchema.parseAsync('hello world') // => throws error
.safeParse
.safeParse(data:unknown): { success: true; data: T; } | { success: false; error: ZodError; }
If you don't want Zod to throw errors when validation fails, use .safeParse
. This method returns an object containing either the successfully parsed data or a ZodError instance containing detailed information about the validation problems.
stringSchema.safeParse(12)
// => { success: false; error: ZodError }
stringSchema.safeParse('billie')
// => { success: true; data: 'billie' }
The result is a discriminated union, so you can handle errors very conveniently:
const result = stringSchema.safeParse('billie')
if (!result.success) {
// handle error then return
result.error
} else {
// do something
result.data
}
.safeParseAsync
Alias:
.spa
An asynchronous version of safeParse
.
await stringSchema.safeParseAsync('billie')
For convenience, this has been aliased to .spa
:
await stringSchema.spa('billie')
.refine
.refine(validator: (data:T)=>any, params?: RefineParams)
Zod lets you provide custom validation logic via refinements. (For advanced features like creating multiple issues and customizing error codes, see .superRefine
.)
Zod was designed to mirror TypeScript as closely as possible. But there are many so-called "refinement types" you may wish to check for that can't be represented in TypeScript's type system. For instance: checking that a number is an integer or that a string is a valid email address.
For example, you can define a custom validation check on any Zod schema with .refine
:
const myString = z.string().refine((val) => val.length <= 255, {
message: "String can't be more than 255 characters",
})
⚠️ Refinement functions should not throw. Instead they should return a falsy value to signal failure.
Arguments
As you can see, .refine
takes two arguments.
- The first is the validation function. This function takes one input (of type
T
— the inferred type of the schema) and returnsany
. Any truthy value will pass validation. (Prior to [email protected] the validation function had to return a boolean.) - The second argument accepts some options. You can use this to customize certain error-handling behavior:
type RefineParams = {
// override error message
message?: string
// appended to error path
path?: (string | number)[]
// params object you can use to customize message
// in error map
params?: object
}
For advanced cases, the second argument can also be a function that returns RefineParams
.
const longString = z.string().refine(
(val) => val.length > 10,
(val) => ({ message: `${val} is not more than 10 characters` }),
)
Customize error path
const passwordForm = z
.object({
password: z.string(),
confirm: z.string(),
})
.refine((data) => data.password === data.confirm, {
message: "Passwords don't match",
path: ['confirm'], // path of error
})
passwordForm.parse({ password: 'asdf', confirm: 'qwer' })
Because you provided a path
parameter, the resulting error will be:
ZodError {
issues: [{
"code": "custom",
"path": [ "confirm" ],
"message": "Passwords don't match"
}]
}
Asynchronous refinements
Refinements can also be async:
const userId = z.string().refine(async (id) => {
// verify that ID exists in database
return true
})
⚠️ If you use async refinements, you must use the
.parseAsync
method to parse data! Otherwise Zod will throw an error.
Relationship to transforms
Transforms and refinements can be interleaved:
z.string()
.transform((val) => val.length)
.refine((val) => val > 25)
.superRefine
The .refine
method is actually syntactic sugar atop a more versatile (and verbose) method called superRefine
. Here's an example:
const Strings = z.array(z.string()).superRefine((val, ctx) => {
if (val.length > 3) {
ctx.addIssue({
code: z.ZodIssueCode.too_big,
maximum: 3,
type: 'array',
inclusive: true,
message: 'Too many items 😡',
})
}
if (val.length !== new Set(val).size) {
ctx.addIssue({
code: z.ZodIssueCode.custom,
message: `No duplicates allowed.`,
})
}
})
You can add as many issues as you like. If ctx.addIssue
is not called during the execution of the function, validation passes.
Normally refinements always create issues with a ZodIssueCode.custom
error code, but with superRefine
it's possible to throw issues of any ZodIssueCode
. Each issue code is described in detail in the Error Handling guide: ERROR_HANDLING.md.
Abort early
By default, parsing will continue even after a refinement check fails. For instance, if you chain together multiple refinements, they will all be executed. However, it may be desirable to abort early to prevent later refinements from being executed. To achieve this, pass the fatal
flag to ctx.addIssue
and return z.NEVER
.
const schema = z.number().superRefine((val, ctx) => {
if (val < 10) {
ctx.addIssue({
code: z.ZodIssueCode.custom,
message: 'should be >= 10',
fatal: true,
})
return z.NEVER
}
if (val !== 12) {
ctx.addIssue({
code: z.ZodIssueCode.custom,
message: 'should be twelve',
})
}
})
Type refinements
If you provide a type predicate to .refine()
or .superRefine()
, the resulting type will be narrowed down to your predicate's type. This is useful if you are mixing multiple chained refinements and transformations:
const schema = z
.object({
first: z.string(),
second: z.number(),
})
.nullable()
.superRefine((arg, ctx): arg is { first: string; second: number } => {
if (!arg) {
ctx.addIssue({
code: z.ZodIssueCode.custom, // customize your issue
message: 'object should exist',
})
}
return z.NEVER // The return value is not used, but we need to return something to satisfy the typing
})
// here, TS knows that arg is not null
.refine((arg) => arg.first === 'bob', '`first` is not `bob`!')
⚠️ You must use
ctx.addIssue()
instead of returning a boolean value to indicate whether the validation passes. Ifctx.addIssue
is not called during the execution of the function, validation passes.
.transform
To transform data after parsing, use the transform
method.
const stringToNumber = z.string().transform((val) => val.length)
stringToNumber.parse('string') // => 6
Chaining order
Note that stringToNumber
above is an instance of the ZodEffects
subclass. It is NOT an instance of ZodString
. If you want to use the built-in methods of ZodString
(e.g. .email()
) you must apply those methods before any transforms.
const emailToDomain = z
.string()
.email()
.transform((val) => val.split('@')[1])
emailToDomain.parse('[email protected]') // => example.com
Validating during transform
The .transform
method can simultaneously validate and transform the value. This is often simpler and less duplicative than chaining transform
and refine
.
As with .superRefine
, the transform function receives a ctx
object with an addIssue
method that can be used to register validation issues.
const numberInString = z.string().transform((val, ctx) => {
const parsed = parseInt(val)
if (isNaN(parsed)) {
ctx.addIssue({
code: z.ZodIssueCode.custom,
message: 'Not a number',
})
// This is a special symbol you can use to
// return early from the transform function.
// It has type `never` so it does not affect the
// inferred return type.
return z.NEVER
}
return parsed
})
Relationship to refinements
Transforms and refinements can be interleaved. These will be executed in the order they are declared.
const nameToGreeting = z
.string()
.transform((val) => val.toUpperCase())
.refine((val) => val.length > 15)
.transform((val) => `Hello ${val}`)
.refine((val) => val.indexOf('!') === -1)
Async transforms
Transforms can also be async.
const IdToUser = z
.string()
.uuid()
.transform(async (id) => {
return await getUserById(id)
})
⚠️ If your schema contains asynchronous transforms, you must use .parseAsync() or .safeParseAsync() to parse data. Otherwise Zod will throw an error.
.default
You can use transforms to implement the concept of "default values" in Zod.
const stringWithDefault = z.string().default('tuna')
stringWithDefault.parse(undefined) // => "tuna"
Optionally, you can pass a function into .default
that will be re-executed whenever a default value needs to be generated:
const numberWithRandomDefault = z.number().default(Math.random)
numberWithRandomDefault.parse(undefined) // => 0.4413456736055323
numberWithRandomDefault.parse(undefined) // => 0.1871840107401901
numberWithRandomDefault.parse(undefined) // => 0.7223408162401552
Conceptually, this is how Zod processes default values:
- If the input is
undefined
, the default value is returned - Otherwise, the data is parsed using the base schema
.describe
Use .describe()
to add a description
property to the resulting schema.
const documentedString = z.string().describe('A useful bit of text, if you know what to do with it.')
documentedString.description // A useful bit of text…
This can be useful for documenting a field, for example in a JSON Schema using a library like zod-to-json-schema
).
.catch
Use .catch()
to provide a "catch value" to be returned in the event of a parsing error.
const numberWithCatch = z.number().catch(42)
numberWithCatch.parse(5) // => 5
numberWithCatch.parse('tuna') // => 42
Optionally, you can pass a function into .catch
that will be re-executed whenever a default value needs to be generated. A ctx
object containing the caught error will be passed into this function.
const numberWithRandomCatch = z.number().catch((ctx) => {
ctx.error // the caught ZodError
return Math.random()
})
numberWithRandomCatch.parse('sup') // => 0.4413456736055323
numberWithRandomCatch.parse('sup') // => 0.1871840107401901
numberWithRandomCatch.parse('sup') // => 0.7223408162401552
Conceptually, this is how Zod processes "catch values":
- The data is parsed using the base schema
- If the parsing fails, the "catch value" is returned
.optional
A convenience method that returns an optional version of a schema.
const optionalString = z.string().optional() // string | undefined
// equivalent to
z.optional(z.string())
.nullable
A convenience method that returns a nullable version of a schema.
const nullableString = z.string().nullable() // string | null
// equivalent to
z.nullable(z.string())
.nullish
A convenience method that returns a "nullish" version of a schema. Nullish schemas will accept both undefined
and null
. Read more about the concept of "nullish" in the TypeScript 3.7 release notes.
const nullishString = z.string().nullish() // string | null | undefined
// equivalent to
z.string().nullable().optional()
.array
A convenience method that returns an array schema for the given type:
const stringArray = z.string().array() // string[]
// equivalent to
z.array(z.string())
.promise
A convenience method for promise types:
const stringPromise = z.string().promise() // Promise<string>
// equivalent to
z.promise(z.string())
.or
A convenience method for union types.
const stringOrNumber = z.string().or(z.number()) // string | number
// equivalent to
z.union([z.string(), z.number()])
.and
A convenience method for creating intersection types.
const nameAndAge = z.object({ name: z.string() }).and(z.object({ age: z.number() })) // { name: string } & { age: number }
// equivalent to
z.intersection(z.object({ name: z.string() }), z.object({ age: z.number() }))
.brand
.brand<T>() => ZodBranded<this, B>
TypeScript's type system is structural, which means that any two types that are structurally equivalent are considered the same.
type Cat = { name: string }
type Dog = { name: string }
const petCat = (cat: Cat) => {}
const fido: Dog = { name: 'fido' }
petCat(fido) // works fine
In some cases, its can be desirable to simulate nominal typing inside TypeScript. For instance, you may wish to write a function that only accepts an input that has been validated by Zod. This can be achieved with branded types (AKA opaque types).
const Cat = z.object({ name: z.string() }).brand<'Cat'>()
type Cat = z.infer<typeof Cat>
const petCat = (cat: Cat) => {}
// this works
const simba = Cat.parse({ name: 'simba' })
petCat(simba)
// this doesn't
petCat({ name: 'fido' })
Under the hood, this works by attaching a "brand" to the inferred type using an intersection type. This way, plain/unbranded data structures are no longer assignable to the inferred type of the schema.
const Cat = z.object({ name: z.string() }).brand<'Cat'>()
type Cat = z.infer<typeof Cat>
// {name: string} & {[symbol]: "Cat"}
Note that branded types do not affect the runtime result of .parse
. It is a static-only construct.
.readonly
.readonly() => ZodReadonly<this>
This method returns a ZodReadonly
schema instance that parses the input using the base schema, then calls Object.freeze()
on the result. The inferred type is also marked as readonly
.
const schema = z.object({ name: string }).readonly()
type schema = z.infer<typeof schema>
// Readonly<{name: string}>
const result = schema.parse({ name: 'fido' })
result.name = 'simba' // error
The inferred type uses TypeScript's built-in readonly types when relevant.
z.array(z.string()).readonly()
// readonly string[]
z.tuple([z.string(), z.number()]).readonly()
// readonly [string, number]
z.map(z.string(), z.date()).readonly()
// ReadonlyMap<string, Date>
z.set(z.string()).readonly()
// ReadonlySet<Promise<string>>
.pipe
Schemas can be chained into validation "pipelines". It's useful for easily validating the result after a .transform()
:
z.string()
.transform((val) => val.length)
.pipe(z.number().min(5))
The .pipe()
method returns a ZodPipeline
instance.
You can use .pipe()
to fix common issues with z.coerce
.
You can constrain the input to types that work well with your chosen coercion. Then use .pipe()
to apply the coercion.
without constrained input:
const toDate = z.coerce.date()
// works intuitively
console.log(toDate.safeParse('2023-01-01').success) // true
// might not be what you want
console.log(toDate.safeParse(null).success) // true
with constrained input:
const datelike = z.union([z.number(), z.string(), z.date()])
const datelikeToDate = datelike.pipe(z.coerce.date())
// still works intuitively
console.log(datelikeToDate.safeParse('2023-01-01').success) // true
// more likely what you want
console.log(datelikeToDate.safeParse(null).success) // false
You can also use this technique to avoid coercions that throw uncaught errors.
without constrained input:
const toBigInt = z.coerce.bigint()
// works intuitively
console.log(toBigInt.safeParse('42')) // true
// probably not what you want
console.log(toBigInt.safeParse(null)) // throws uncaught error
with constrained input:
const toNumber = z.number().or(z.string()).pipe(z.coerce.number())
const toBigInt = z.bigint().or(toNumber).pipe(z.coerce.bigint())
// still works intuitively
console.log(toBigInt.safeParse('42').success) // true
// error handled by zod, more likely what you want
console.log(toBigInt.safeParse(null).success) // false
Guides and concepts
Type inference
You can extract the TypeScript type of any schema with z.infer<typeof mySchema>
.
const A = z.string()
type A = z.infer<typeof A> // string
const u: A = 12 // TypeError
const u: A = 'asdf' // compiles
What about transforms?
In reality each Zod schema internally tracks two types: an input and an output. For most schemas (e.g. z.string()
) these two are the same. But once you add transforms into the mix, these two values can diverge. For instance z.string().transform(val => val.length)
has an input of string
and an output of number
.
You can separately extract the input and output types like so:
const stringToNumber = z.string().transform((val) => val.length)
// ⚠️ Important: z.infer returns the OUTPUT type!
type input = z.input<typeof stringToNumber> // string
type output = z.output<typeof stringToNumber> // number
// equivalent to z.output!
type inferred = z.infer<typeof stringToNumber> // number
Writing generic functions
With TypeScript generics, you can write reusable functions that accept Zod schemas as parameters. This enables you to create custom validation logic, schema transformations, and more, while maintaining type safety and inference.
When attempting to write a function that accepts a Zod schema as an input, it's tempting to try something like this:
function inferSchema<T>(schema: z.ZodType<T>) {
return schema
}
This approach is incorrect, and limits TypeScript's ability to properly infer the argument. No matter what you pass in, the type of schema
will be an instance of ZodType
.
inferSchema(z.string())
// => ZodType<string>
This approach loses type information, namely which subclass the input actually is (in this case, ZodString
). That means you can't call any string-specific methods like .min()
on the result of inferSchema
.
A better approach is to infer the schema as a whole instead of merely its inferred type. You can do this with a utility type called z.ZodTypeAny
.
function inferSchema<T extends z.ZodTypeAny>(schema: T) {
return schema
}
inferSchema(z.string())
// => ZodString
ZodTypeAny
is just a shorthand forZodType<any, any, any>
, a type that is broad enough to match any Zod schema.
The Result is now fully and properly typed, and the type system can infer the specific subclass of the schema.
Inferring the inferred type
If you follow the best practice of using z.ZodTypeAny
as the generic parameter for your schema, you may encounter issues with the parsed data being typed as any
instead of the inferred type of the schema.
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