createParser

Wrap a set of parse/serialize functions into a builder pattern parser for use with nuqs hooks.

export function createParser<T>(
  parser: Require<SingleParser<T>, 'parse' | 'serialize'>
): SingleParserBuilder<T>

From: packages/nuqs/src/parsers.ts:150-193

Parameters

object

required

Parser configuration object.

Show properties

(value: string) => T | null

required

Function to convert a URL query string value into a typed state value.Must return null for invalid inputs to ensure graceful degradation.

(value: T) => string

required

Function to convert a typed state value back into a URL query string.Must be lossless - serializing and then parsing should return the original value.

(a: T, b: T) => boolean

Custom equality function for comparing state values.Defaults to referential equality (a === b). Provide this when parsing objects or arrays.

Returns

object

A parser builder with the following methods and properties:

Show properties

(value: string) => T | null

The parse function from the input.

(value: T) => string

The serialize function from the input.

(a: T, b: T) => boolean

Equality function (defaults to (a, b) => a === b).

'single'

Parser type identifier.

(defaultValue: NonNullable<T>) => SingleParserBuilder<T>

Returns a new parser with a default value, making the hook state non-nullable.Setting state to the default value clears the query parameter from the URL (unless clearOnDefault: false).

(options: Options) => this

Returns the parser with navigation options (history, scroll, shallow, etc.) pre-configured.

(value: string | string[] | undefined) => T | null

Server-side parsing helper (deprecated in favor of loaders).

Usage

Basic Custom Parser

import { createParser } from 'nuqs'

const parseAsHexColor = createParser({
  parse(query: string) {
    // Validate hex color format
    if (!/^[0-9A-Fa-f]{6}$/.test(query)) {
      return null // Invalid format
    }
    return `#${query}`
  },
  serialize(value: string) {
    // Remove # prefix for URL
    return value.replace('#', '')
  }
})

const [color, setColor] = useQueryState(
  'color',
  parseAsHexColor.withDefault('#ff0000')
)
// URL: ?color=ff0000
// State: '#ff0000'

setColor('#00ff00')
// URL: ?color=00ff00

Parser with Custom Equality

import { createParser } from 'nuqs'

type Point = { x: number; y: number }

const parseAsPoint = createParser({
  parse(query: string) {
    const match = query.match(/^(\d+),(\d+)$/)
    if (!match) return null
    return {
      x: parseInt(match[1]),
      y: parseInt(match[2])
    }
  },
  serialize(value: Point) {
    return `${value.x},${value.y}`
  },
  eq(a: Point, b: Point) {
    // Deep equality for objects
    return a.x === b.x && a.y === b.y
  }
})

const [cursor, setCursor] = useQueryState(
  'cursor',
  parseAsPoint.withDefault({ x: 0, y: 0 })
)
// URL: ?cursor=100,200
// State: { x: 100, y: 200 }

Composing Existing Parsers

import { createParser, parseAsHex } from 'nuqs'

type RGB = { r: number; g: number; b: number }

const parseAsRgb = createParser({
  parse(query: string) {
    if (query.length !== 6) {
      return null
    }
    return {
      r: parseAsHex.parse(query.slice(0, 2)) ?? 0x00,
      g: parseAsHex.parse(query.slice(2, 4)) ?? 0x00,
      b: parseAsHex.parse(query.slice(4)) ?? 0x00
    }
  },
  serialize({ r, g, b }: RGB) {
    return (
      parseAsHex.serialize(r) +
      parseAsHex.serialize(g) +
      parseAsHex.serialize(b)
    )
  },
  eq(a, b) {
    return a.r === b.r && a.g === b.g && a.b === b.b
  }
})

const [color, setColor] = useQueryState(
  'color',
  parseAsRgb.withDefault({ r: 255, g: 0, b: 0 })
)
// URL: ?color=ff0000
// State: { r: 255, g: 0, b: 0 }

Parser with Validation

import { createParser } from 'nuqs'

const parseAsEmail = createParser({
  parse(query: string) {
    // Basic email validation
    const emailRegex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/
    if (!emailRegex.test(query)) {
      return null
    }
    return query
  },
  serialize: String
})

const [email, setEmail] = useQueryState('email', parseAsEmail)
// URL: ?email=user@example.com
// State: 'user@example.com'

// URL: ?email=invalid-email
// State: null (validation failed)

Builder Methods

withDefault

Set a default value to make the hook state non-nullable.

const parser = createParser({
  parse: v => parseInt(v) || null,
  serialize: String
})

const parserWithDefault = parser.withDefault(0)

// Without default
const [count1, setCount1] = useQueryState('count', parser)
// Type: number | null

// With default
const [count2, setCount2] = useQueryState('count', parserWithDefault)
// Type: number (never null)

Behavior:

When URL has no value: returns default instead of null
When setting to default: clears query parameter from URL (unless clearOnDefault: false)
When setting to null: clears query parameter and returns default value

From: packages/nuqs/src/parsers.ts:79-103

withOptions

Pre-configure navigation options at the parser level.

const parser = createParser({
  parse: v => v,
  serialize: String
})

const parserWithOptions = parser
  .withOptions({
    history: 'push',  // Create new history entry
    scroll: true,     // Scroll to top on update
    shallow: false    // Trigger server request
  })

const [search, setSearch] = useQueryState('q', parserWithOptions)
// Every update uses these options

// Options can still be overridden per update
setSearch('query', { history: 'replace' })

Available Options:

history: 'push' | 'replace' - How updates affect browser history
scroll: boolean - Scroll to top after update
shallow: boolean - Client-only updates (default: true)
throttleMs: number - Throttle URL updates (deprecated, use limitUrlUpdates)
limitUrlUpdates: Rate limit configuration
startTransition: React transition function
clearOnDefault: boolean - Clear URL when setting to default (default: true)

From: packages/nuqs/src/parsers.ts:61-62 and packages/nuqs/src/parsers.ts:186-192

Chaining Methods

Builder methods can be chained in any order:

const parser = parseAsInteger
  .withDefault(1)
  .withOptions({ history: 'push' })
  .withOptions({ scroll: true })
  .withDefault(10) // Overrides previous default

const [page, setPage] = useQueryState('page', parser)
// Type: number (default: 10)
// Options: { history: 'push', scroll: true }

Implementation Details

Full Implementation

export function createParser<T>(
  parser: Require<SingleParser<T>, 'parse' | 'serialize'>
): SingleParserBuilder<T> {
  function parseServerSideNullable(value: string | string[] | undefined) {
    if (typeof value === 'undefined') {
      return null
    }
    let str = ''
    if (Array.isArray(value)) {
      // Follow the spec:
      // https://url.spec.whatwg.org/#dom-urlsearchparams-get
      if (value[0] === undefined) {
        return null
      }
      str = value[0]
    }
    if (typeof value === 'string') {
      str = value
    }
    return safeParse(parser.parse, str)
  }

  return {
    type: 'single',
    eq: (a, b) => a === b,
    ...parser,
    parseServerSide: parseServerSideNullable,
    withDefault(defaultValue) {
      return {
        ...this,
        defaultValue,
        parseServerSide(value) {
          return parseServerSideNullable(value) ?? defaultValue
        }
      }
    },
    withOptions(options: Options) {
      return {
        ...this,
        ...options
      }
    }
  }
}

From: packages/nuqs/src/parsers.ts:150-193

safeParse Helper

The safeParse helper wraps the parse function to handle errors gracefully:

// From packages/nuqs/src/lib/safe-parse.ts
function safeParse<T>(
  parse: (value: string) => T | null,
  value: string,
  path?: string
): T | null {
  try {
    return parse(value)
  } catch (error) {
    console.error(`[nuqs] Parse error${path ? ` at ${path}` : ''}:`, error)
    return null
  }
}

Best Practices

1. Always Return Null for Invalid Input

// ✅ Good
const parseAsPositiveInt = createParser({
  parse(v) {
    const num = parseInt(v)
    if (num > 0) return num
    return null // Invalid: negative or NaN
  },
  serialize: String
})

// ❌ Bad - throws errors
const parseAsPositiveInt = createParser({
  parse(v) {
    const num = parseInt(v)
    if (num <= 0) throw new Error('Must be positive')
    return num
  },
  serialize: String
})

2. Ensure Lossless Serialization

// ✅ Good - preserves precision
const parseAsFloat = createParser({
  parse(v) {
    const num = parseFloat(v)
    return num == num ? num : null
  },
  serialize: String // No data loss
})

// ❌ Bad - loses precision
const parseAsFloat = createParser({
  parse: parseFloat,
  serialize: v => v.toFixed(2) // Rounds to 2 decimals!
})

3. Provide Custom Equality for Objects

// ✅ Good - custom equality
const parseAsRange = createParser({
  parse(v) {
    const [min, max] = v.split('-').map(Number)
    return { min, max }
  },
  serialize: ({ min, max }) => `${min}-${max}`,
  eq: (a, b) => a.min === b.min && a.max === b.max
})

// ❌ Bad - referential equality won't work
const parseAsRange = createParser({
  parse(v) {
    const [min, max] = v.split('-').map(Number)
    return { min, max }
  },
  serialize: ({ min, max }) => `${min}-${max}`
  // Missing eq - clearOnDefault won't work correctly
})

4. Use Type Guards for Complex Types

type Status = 'pending' | 'active' | 'completed'

const isStatus = (value: unknown): value is Status => {
  return ['pending', 'active', 'completed'].includes(value as string)
}

const parseAsStatus = createParser({
  parse(query): Status | null {
    return isStatus(query) ? query : null
  },
  serialize: String
})

createMultiParser

For creating multi-value parsers (e.g., ?tag=a&tag=b):

export function createMultiParser<T>(
  parser: Omit<Require<MultiParser<T>, 'parse' | 'serialize'>, 'type'>
): MultiParserBuilder<T>

From: packages/nuqs/src/parsers.ts:195-226 Usage:

import { createMultiParser, parseAsInteger } from 'nuqs'

const parseAsIntArray = createMultiParser({
  parse: (values: readonly string[]) => {
    const parsed = values.map(v => parseAsInteger.parse(v)).filter(v => v !== null)
    return parsed.length > 0 ? parsed : null
  },
  serialize: (values: number[]) => values.map(String)
})

const [ids, setIds] = useQueryState('id', parseAsIntArray.withDefault([]))
// URL: ?id=1&id=2&id=3
// State: [1, 2, 3]

Next Steps

Built-in Parsers - Reference for all built-in parsers
Parser System Overview - Understand parser architecture
Parser Concepts - Higher-level usage guide

Hooks

Parsers

Server Utilities

Testing

Types

createParser

createParser

Parameters

Returns

Usage

Basic Custom Parser

Parser with Custom Equality

Composing Existing Parsers

Parser with Validation

Builder Methods

withDefault

withOptions

Chaining Methods

Implementation Details

Full Implementation

safeParse Helper

Best Practices

1. Always Return Null for Invalid Input

2. Ensure Lossless Serialization

3. Provide Custom Equality for Objects

4. Use Type Guards for Complex Types

createMultiParser

Next Steps

​createParser

​Parameters

​Returns

​Usage

​Basic Custom Parser

​Parser with Custom Equality

​Composing Existing Parsers

​Parser with Validation

​Builder Methods

​withDefault

​withOptions

​Chaining Methods

​Implementation Details

​Full Implementation

​safeParse Helper

​Best Practices

​1. Always Return Null for Invalid Input

​2. Ensure Lossless Serialization

​3. Provide Custom Equality for Objects

​4. Use Type Guards for Complex Types

​Related APIs

​createMultiParser

​Next Steps

createParser

Parameters

Returns

Usage

Basic Custom Parser

Parser with Custom Equality

Composing Existing Parsers

Parser with Validation

Builder Methods

withDefault

withOptions

Chaining Methods

Implementation Details

Full Implementation

safeParse Helper

Best Practices

1. Always Return Null for Invalid Input

2. Ensure Lossless Serialization

3. Provide Custom Equality for Objects

4. Use Type Guards for Complex Types

Related APIs

createMultiParser

Next Steps