qs-ts

A focused TypeScript library for parsing and stringifying URL query strings with predictable behavior, explicit typing controls, and practical defaults.

Features

• Predictable Parsing: Explicit control over numbers, booleans, arrays, and per-key types so query values resolve the way you expect
• Practical Array Handling: Built-in support for repeated keys and comma-separated values, including configurable handling for encoded commas
• Built for Typed Codebases: First-class TypeScript definitions with typed parse options and value casting
• Safe by Default: Gracefully handles malformed encodings and avoids surprising coercion
• Flexible Serialization: Configure encoding, null behavior, empty strings, and array output to match your API
• Ready Everywhere: Works in both ESM and CommonJS environments

Installation

npm install qs-ts

💡 Consider using the native browser API URLSearchParams for simple use cases.

Usage

Basic Parsing

import { parse } from 'qs-ts';

const result = parse('a=1&b=hello&c=true');
console.log(result);
// { a: '1', b: 'hello', c: 'true' } -> by default everything is a string

Basic Stringifying

import { stringify } from 'qs-ts';

const query = stringify({ a: 1, b: 'hello', c: true });
console.log(query);
// 'a=1&b=hello&c=true'

CommonJS

const { parse, stringify } = require('qs-ts');

API

parse(query: string, options?: ParseOptions): Record<string, any>

Parses a query string into an object.

Options

Option	Type	Default	Description
decode	boolean	true	Decode percent-encoded characters.
parseNumber	boolean	false	Parse numeric-looking values with Number(...); does not parse Infinity, NaN, or empty strings.
parseBoolean	boolean	false	Parse only lowercase "true" / "false" to booleans.
array	ParseArrayFormat	{ format: "repeat" }	How arrays are represented in the query string.
types	Record<string, ValueType>	undefined	Explicit per-key typing; takes priority over global parse flags.
onTypeError	ValueTypeError	"keep"	Behavior when explicit types casting fails.

 

Parse Options Definition:

type ParseOptions = {
	decode?: boolean;
	array?: ParseArrayFormat;
	parseNumber?: boolean;
	parseBoolean?: boolean;
	types?: Record<string, ValueType>;
	onTypeError?: ValueTypeError;
};

type ParseArrayFormat =
  | { format: "repeat" }
  | { format: "comma"; encoded: "preserve" | "split" };

array behavior for comma format:

⚠️ Comma separated arrays depend on delimiter consistency. If values may be URL encoded or come from external sources, repeat is safer and more predictable.

• encoded: "preserve" splits on literal , only; %2C is treated as data.
• encoded: "split" splits on literal , and on %2C/%2c so results don’t depend on upstream encoding.

type ValueType =
	| "string"
	| "number"
	| "boolean"
	| "string[]"
	| "number[]";

type ValueTypeError = "keep" | "throw" | "drop";

onTypeError behavior with explicit types:

• "keep": keep the invalid value (for arrays, keep the invalid item).
• "drop": remove the invalid value (for arrays, drop the invalid item).
• "throw": throw TypeError.

Examples

Parsing Numbers and Booleans

parse('a=1&b=true&c=null', { parseNumber: true, parseBoolean: true });
// { a: 1, b: true, c: 'null' } (null literal not parsed unless typed)

parse('d=hello&e=001&f=12.5', { parseNumber: true });
// { d: 'hello', e: 1, f: 12.5 }

Array Formats

// Repeat (default)
parse('tags=a&tags=b');
// { tags: ['a', 'b'] }

// Comma (Preserve encoded commas)
parse('tags=a,b%2Cc', { array: { format: 'comma', encoded: 'preserve' } });
// { tags: ['a', 'b,c'] }

// Comma (Split encoded commas)
parse('tags=a,b%2Cc', { array: { format: 'comma', encoded: 'split' } });
// { tags: ['a', 'b', 'c'] }

Explicit Types

Explicit types take priority over all global parse rules (array, parseNumber, parseBoolean) on a per-key basis. If a key has an explicit scalar type (string, number, boolean), it is treated as scalar for that key (for repeated params, the last value wins before casting). If a key has an explicit array type (string[], number[]), array behavior applies for that key. If a key has no explicit type, global rules apply.

parse('count=5&flags=on&items=a&items=b', {
  parseNumber: true,
  parseBoolean: true,
  types: { count: 'string', flags: 'boolean', items: 'string[]' }
});
// { count: '5', flags: true, items: ['a', 'b'] }
// count stays string because of explicit type, despite parseNumber: true

Decoding Control

parse('q=hello%20world', { decode: true });
// { q: 'hello world' }

parse('q=hello%20world', { decode: false });
// { q: 'hello%20world' }

stringify(object: Record<string, any>, options?: StringifyOptions): string

Serializes an object into a query string.

Options

Option	Type	Default	Description
encode	boolean	true	Encode special characters.
array	StringifyArrayFormat	{ format: "repeat" }	How arrays are serialized.
skipNull	boolean	false	Skip null values (or null array items).
skipEmptyString	boolean	false	Skip empty-string values (or empty-string array items).

 

Stringify Options Definition:

type StringifyOptions = {
	encode?: boolean;
	array?: StringifyArrayFormat;
	skipNull?: boolean;
	skipEmptyString?: boolean;
};

type StringifyArrayFormat =
  | { format: "repeat" }
  | { format: "comma" };

Examples

Basic Usage

stringify({ a: 1, b: 'hello', c: true });
// 'a=1&b=hello&c=true'

Array Formats

// Repeat (default)
stringify({ tags: ['a', 'b', 'c'] });
// 'tags=a&tags=b&tags=c'

// Comma
stringify({ tags: ['a', 'b', 'c'] }, { array: { format: 'comma' } });
// 'tags=a,b,c'

Skipping Values

stringify({ a: 1, b: null, c: '', d: undefined }, { skipNull: true, skipEmptyString: true });
// 'a=1'

stringify({ a: 1, b: null }, { skipNull: false });
// 'a=1&b'

Encoding Control

stringify({ q: 'hello world' }, { encode: true });
// 'q=hello%20world'

stringify({ q: 'hello world' }, { encode: false });
// 'q=hello world'

Advanced Examples

Complex Objects

Note: Nested objects are not supported. They are converted to their string representation.

const obj = {
  user: 'john',
  age: 30,
  active: true,
  tags: ['developer', 'typescript'],
  metadata: {
    created: '2025-01-01'  // This nested object will become '[object Object]'
  }
};

const query = stringify(obj, { array: { format: 'repeat' } });
console.log(query);
// 'user=john&age=30&active=true&tags=developer&tags=typescript&metadata=%5Bobject%20Object%5D'

// When parsing back, you might want numeric/boolean values restored:
const parsed = parse(query, {
  parseNumber: true,
  parseBoolean: true,
  array: { format: 'repeat' }
});
console.log(parsed);
// { user: 'john', age: 30, active: true, tags: ['developer', 'typescript'], metadata: '[object Object]' }

URL Integration

// Parse from URL with repeat format (default)
const url2 = new URL('https://example.com/search?q=typescript&tags=web&tags=api&limit=10');
// Use explicit global parse flags as needed
const params2 = parse(url2.search.slice(1), { parseNumber: true, array: { format: 'repeat' } });
console.log(params2);
// { q: 'typescript', tags: ['web', 'api'], limit: 10 }

// Parse from URL with comma format
const url3 = new URL('https://example.com/search?q=typescript&tags=web,api&limit=10');
const params3 = parse(url3.search.slice(1), { parseNumber: true, array: { format: 'comma', encoded: 'preserve' } });
console.log(params3);
// { q: 'typescript', tags: ['web', 'api'], limit: 10 }

// Build URL
const baseUrl = 'https://example.com/search';
const queryString = stringify({ q: 'javascript', sort: 'recent' });
const fullUrl = `${baseUrl}?${queryString}`;
console.log(fullUrl);
// 'https://example.com/search?q=javascript&sort=recent'

Development

Building

bun run build

Testing

bun test

Verification

node verify.mjs
# or
bun verify.mjs

License

MIT - see LICENSE