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Query string

Stability: 3 - Legacy

The querystring module provides utilities for parsing and formatting URL query strings. It can be accessed using:

const querystring = require('querystring');

The querystring API is considered Legacy. While it is still maintained, new code should use the {URLSearchParams} API instead.

querystring.decode()

The querystring.decode() function is an alias for querystring.parse().

querystring.encode()

The querystring.encode() function is an alias for querystring.stringify().

querystring.escape(str)

  • str {string}

The querystring.escape() method performs URL percent-encoding on the given str in a manner that is optimized for the specific requirements of URL query strings.

The querystring.escape() method is used by querystring.stringify() and is generally not expected to be used directly. It is exported primarily to allow application code to provide a replacement percent-encoding implementation if necessary by assigning querystring.escape to an alternative function.

querystring.parse(str[, sep[, eq[, options]]])

  • str {string} The URL query string to parse
  • sep {string} The substring used to delimit key and value pairs in the query string. Default: '&'.
  • eq {string}. The substring used to delimit keys and values in the query string. Default: '='.
  • options {Object}
    • decodeURIComponent {Function} The function to use when decoding percent-encoded characters in the query string. Default: querystring.unescape().
    • maxKeys {number} Specifies the maximum number of keys to parse. Specify 0 to remove key counting limitations. Default: 1000.

The querystring.parse() method parses a URL query string (str) into a collection of key and value pairs.

For example, the query string 'foo=bar&abc=xyz&abc=123' is parsed into:

{
  foo: 'bar',
  abc: ['xyz', '123']
}

The object returned by the querystring.parse() method does not prototypically inherit from the JavaScript Object. This means that typical Object methods such as obj.toString(), obj.hasOwnProperty(), and others are not defined and will not work.

By default, percent-encoded characters within the query string will be assumed to use UTF-8 encoding. If an alternative character encoding is used, then an alternative decodeURIComponent option will need to be specified:

// Assuming gbkDecodeURIComponent function already exists...

querystring.parse('w=%D6%D0%CE%C4&foo=bar', null, null,
                  { decodeURIComponent: gbkDecodeURIComponent });

querystring.stringify(obj[, sep[, eq[, options]]])

  • obj {Object} The object to serialize into a URL query string
  • sep {string} The substring used to delimit key and value pairs in the query string. Default: '&'.
  • eq {string}. The substring used to delimit keys and values in the query string. Default: '='.
  • options
    • encodeURIComponent {Function} The function to use when converting URL-unsafe characters to percent-encoding in the query string. Default: querystring.escape().

The querystring.stringify() method produces a URL query string from a given obj by iterating through the object's "own properties".

It serializes the following types of values passed in obj: {string|number|bigint|boolean|string[]|number[]|bigint[]|boolean[]} The numeric values must be finite. Any other input values will be coerced to empty strings.

querystring.stringify({ foo: 'bar', baz: ['qux', 'quux'], corge: '' });
// Returns 'foo=bar&baz=qux&baz=quux&corge='

querystring.stringify({ foo: 'bar', baz: 'qux' }, ';', ':');
// Returns 'foo:bar;baz:qux'

By default, characters requiring percent-encoding within the query string will be encoded as UTF-8. If an alternative encoding is required, then an alternative encodeURIComponent option will need to be specified:

// Assuming gbkEncodeURIComponent function already exists,

querystring.stringify({ w: '中文', foo: 'bar' }, null, null,
                      { encodeURIComponent: gbkEncodeURIComponent });

querystring.unescape(str)

  • str {string}

The querystring.unescape() method performs decoding of URL percent-encoded characters on the given str.

The querystring.unescape() method is used by querystring.parse() and is generally not expected to be used directly. It is exported primarily to allow application code to provide a replacement decoding implementation if necessary by assigning querystring.unescape to an alternative function.

By default, the querystring.unescape() method will attempt to use the JavaScript built-in decodeURIComponent() method to decode. If that fails, a safer equivalent that does not throw on malformed URLs will be used.