# qs <sup>[![Version Badge][npm-version-svg]][package-url]</sup>

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A querystring parsing and stringifying library with some added security.

Lead Maintainer: [Jordan Harband](https://github.com/ljharb)

The **qs** module was originally created and maintained by [TJ Holowaychuk](https://github.com/visionmedia/node-querystring).

## Usage

```javascript
var qs = require('qs');
var assert = require('assert');

var obj = qs.parse('a=c');
assert.deepEqual(obj, { a: 'c' });

var str = qs.stringify(obj);
assert.equal(str, 'a=c');
```

### Parsing Objects

[](#preventEval)
```javascript
qs.parse(string, [options]);
```

**qs** allows you to create nested objects within your query strings, by surrounding the name of sub-keys with square brackets `[]`.
For example, the string `'foo[bar]=baz'` converts to:

```javascript
assert.deepEqual(qs.parse('foo[bar]=baz'), {
    foo: {
        bar: 'baz'
    }
});
```

When using the `plainObjects` option the parsed value is returned as a null object, created via `Object.create(null)` and as such you should be aware that prototype methods will not exist on it and a user may set those names to whatever value they like:

```javascript
var nullObject = qs.parse('a[hasOwnProperty]=b', { plainObjects: true });
assert.deepEqual(nullObject, { a: { hasOwnProperty: 'b' } });
```

By default parameters that would overwrite properties on the object prototype are ignored, if you wish to keep the data from those fields either use `plainObjects` as mentioned above, or set `allowPrototypes` to `true` which will allow user input to overwrite those properties. *WARNING* It is generally a bad idea to enable this option as it can cause problems when attempting to use the properties that have been overwritten. Always be careful with this option.

```javascript
var protoObject = qs.parse('a[hasOwnProperty]=b', { allowPrototypes: true });
assert.deepEqual(protoObject, { a: { hasOwnProperty: 'b' } });
```

URI encoded strings work too:

```javascript
assert.deepEqual(qs.parse('a%5Bb%5D=c'), {
    a: { b: 'c' }
});
```

You can also nest your objects, like `'foo[bar][baz]=foobarbaz'`:

```javascript
assert.deepEqual(qs.parse('foo[bar][baz]=foobarbaz'), {
    foo: {
        bar: {
            baz: 'foobarbaz'
        }
    }
});
```

By default, when nesting objects **qs** will only parse up to 5 children deep. This means if you attempt to parse a string like
`'a[b][c][d][e][f][g][h][i]=j'` your resulting object will be:

```javascript
var expected = {
    a: {
        b: {
            c: {
                d: {
                    e: {
                        f: {
                            '[g][h][i]': 'j'
                        }
                    }
                }
            }
        }
    }
};
var string = 'a[b][c][d][e][f][g][h][i]=j';
assert.deepEqual(qs.parse(string), expected);
```

This depth can be overridden by passing a `depth` option to `qs.parse(string, [options])`:

```javascript
var deep = qs.parse('a[b][c][d][e][f][g][h][i]=j', { depth: 1 });
assert.deepEqual(deep, { a: { b: { '[c][d][e][f][g][h][i]': 'j' } } });
```

The depth limit helps mitigate abuse when **qs** is used to parse user input, and it is recommended to keep it a reasonably small number.

For similar reasons, by default **qs** will only parse up to 1000 parameters. This can be overridden by passing a `parameterLimit` option:

```javascript
var limited = qs.parse('a=b&c=d', { parameterLimit: 1 });
assert.deepEqual(limited, { a: 'b' });
```

To bypass the leading question mark, use `ignoreQueryPrefix`:

```javascript
var prefixed = qs.parse('?a=b&c=d', { ignoreQueryPrefix: true });
assert.deepEqual(prefixed, { a: 'b', c: 'd' });
```

An optional delimiter can also be passed:

```javascript
var delimited = qs.parse('a=b;c=d', { delimiter: ';' });
assert.deepEqual(delimited, { a: 'b', c: 'd' });
```

Delimiters can be a regular expression too:

```javascript
var regexed = qs.parse('a=b;c=d,e=f', { delimiter: /[;,]/ });
assert.deepEqual(regexed, { a: 'b', c: 'd', e: 'f' });
```

Option `allowDots` can be used to enable dot notation:

```javascript
var withDots = qs.parse('a.b=c', { allowDots: true });
assert.deepEqual(withDots, { a: { b: 'c' } });
```

If you have to deal with legacy browsers or services, there's
also support for decoding percent-encoded octets as iso-8859-1:

```javascript
var oldCharset = qs.parse('a=%A7', { charset: 'iso-8859-1' });
assert.deepEqual(oldCharset, { a: '§' });
```

Some services add an initial `utf8=✓` value to forms so that old
Internet Explorer versions are more likely to submit the form as
utf-8. Additionally, the server can check the value against wrong
encodings of the checkmark character and detect that a query string
or `application/x-www-form-urlencoded` body was *not* sent as
utf-8, eg. if the form had an `accept-charset` parameter or the
containing page had a different character set.

**qs** supports this mechanism via the `charsetSentinel` option.
If specified, the `utf8` parameter will be omitted from the
returned object. It will be used to switch to `iso-8859-1`/`utf-8`
mode depending on how the checkmark is encoded.

**Important**: When you specify both the `charset` option and the
`charsetSentinel` option, the `charset` will be overridden when
the request contains a `utf8` parameter from which the actual
charset can be deduced. In that sense the `charset` will behave
as the default charset rather than the authoritative charset.

```javascript
var detectedAsUtf8 = qs.parse('utf8=%E2%9C%93&a=%C3%B8', {
    charset: 'iso-8859-1',
    charsetSentinel: true
});
assert.deepEqual(detectedAsUtf8, { a: 'ø' });

// Browsers encode the checkmark as &#10003; when submitting as iso-8859-1:
var detectedAsIso8859_1 = qs.parse('utf8=%26%2310003%3B&a=%F8', {
    charset: 'utf-8',
    charsetSentinel: true
});
assert.deepEqual(detectedAsIso8859_1, { a: 'ø' });
```

If you want to decode the `&#...;` syntax to the actual character,
you can specify the `interpretNumericEntities` option as well:

```javascript
var detectedAsIso8859_1 = qs.parse('a=%26%239786%3B', {
    charset: 'iso-8859-1',
    interpretNumericEntities: true
});
assert.deepEqual(detectedAsIso8859_1, { a: '☺' });
```

It also works when the charset has been detected in `charsetSentinel`
mode.

### Parsing Arrays

**qs** can also parse arrays using a similar `[]` notation:

```javascript
var withArray = qs.parse('a[]=b&a[]=c');
assert.deepEqual(withArray, { a: ['b', 'c'] });
```

You may specify an index as well:

```javascript
var withIndexes = qs.parse('a[1]=c&a[0]=b');
assert.deepEqual(withIndexes, { a: ['b', 'c'] });
```

Note that the only difference between an index in an array and a key in an object is that the value between the brackets must be a number
to create an array. When creating arrays with specific indices, **qs** will compact a sparse array to only the existing values preserving
their order:

```javascript
var noSparse = qs.parse('a[1]=b&a[15]=c');
assert.deepEqual(noSparse, { a: ['b', 'c'] });
```

You may also use `allowSparse` option to parse sparse arrays:

```javascript
var sparseArray = qs.parse('a[1]=2&a[3]=5', { allowSparse: true });
assert.deepEqual(sparseArray, { a: [, '2', , '5'] });
```

Note that an empty string is also a value, and will be preserved:

```javascript
var withEmptyString = qs.parse('a[]=&a[]=b');
assert.deepEqual(withEmptyString, { a: ['', 'b'] });

var withIndexedEmptyString = qs.parse('a[0]=b&a[1]=&a[2]=c');
assert.deepEqual(withIndexedEmptyString, { a: ['b', '', 'c'] });
```

**qs** will also limit specifying indices in an array to a maximum index of `20`. Any array members with an index of greater than `20` will
instead be converted to an object with the index as the key. This is needed to handle cases when someone sent, for example, `a[999999999]` and it will take significant time to iterate over this huge array.

```javascript
var withMaxIndex = qs.parse('a[100]=b');
assert.deepEqual(withMaxIndex, { a: { '100': 'b' } });
```

This limit can be overridden by passing an `arrayLimit` option:

```javascript
var withArrayLimit = qs.parse('a[1]=b', { arrayLimit: 0 });
assert.deepEqual(withArrayLimit, { a: { '1': 'b' } });
```

To disable array parsing entirely, set `parseArrays` to `false`.

```javascript
var noParsingArrays = qs.parse('a[]=b', { parseArrays: false });
assert.deepEqual(noParsingArrays, { a: { '0': 'b' } });
```

If you mix notations, **qs** will merge the two items into an object:

```javascript
var mixedNotation = qs.parse('a[0]=b&a[b]=c');
assert.deepEqual(mixedNotation, { a: { '0': 'b', b: 'c' } });
```

You can also create arrays of objects:

```javascript
var arraysOfObjects = qs.parse('a[][b]=c');
assert.deepEqual(arraysOfObjects, { a: [{ b: 'c' }] });
```

Some people use comma to join array, **qs** can parse it:
```javascript
var arraysOfObjects = qs.parse('a=b,c', { comma: true })
assert.deepEqual(arraysOfObjects, { a: ['b', 'c'] })
```
(_this cannot convert nested objects, such as `a={b:1},{c:d}`_)

### Parsing primitive/scalar values (numbers, booleans, null, etc)

By default, all values are parsed as strings. This behavior will not change and is explained in [issue #91](https://github.com/ljharb/qs/issues/91).

```javascript
var primitiveValues = qs.parse('a=15&b=true&c=null');
assert.deepEqual(primitiveValues, { a: '15', b: 'true', c: 'null' });
```

If you wish to auto-convert values which look like numbers, booleans, and other values into their primitive counterparts, you can use the [query-types Express JS middleware](https://github.com/xpepermint/query-types) which will auto-convert all request query parameters.

### Stringifying

[](#preventEval)
```javascript
qs.stringify(object, [options]);
```

When stringifying, **qs** by default URI encodes output. Objects are stringified as you would expect:

```javascript
assert.equal(qs.stringify({ a: 'b' }), 'a=b');
assert.equal(qs.stringify({ a: { b: 'c' } }), 'a%5Bb%5D=c');
```

This encoding can be disabled by setting the `encode` option to `false`:

```javascript
var unencoded = qs.stringify({ a: { b: 'c' } }, { encode: false });
assert.equal(unencoded, 'a[b]=c');
```

Encoding can be disabled for keys by setting the `encodeValuesOnly` option to `true`:
```javascript
var encodedValues = qs.stringify(
    { a: 'b', c: ['d', 'e=f'], f: [['g'], ['h']] },
    { encodeValuesOnly: true }
);
assert.equal(encodedValues,'a=b&c[0]=d&c[1]=e%3Df&f[0][0]=g&f[1][0]=h');
```

This encoding can also be replaced by a custom encoding method set as `encoder` option:

```javascript
var encoded = qs.stringify({ a: { b: 'c' } }, { encoder: function (str) {
    // Passed in values `a`, `b`, `c`
    return // Return encoded string
}})
```

_(Note: the `encoder` option does not apply if `encode` is `false`)_

Analogue to the `encoder` there is a `decoder` option for `parse` to override decoding of properties and values:

```javascript
var decoded = qs.parse('x=z', { decoder: function (str) {
    // Passed in values `x`, `z`
    return // Return decoded string
}})
```

You can encode keys and values using different logic by using the type argument provided to the encoder:

```javascript
var encoded = qs.stringify({ a: { b: 'c' } }, { encoder: function (str, defaultEncoder, charset, type) {
    if (type === 'key') {
        return // Encoded key
    } else if (type === 'value') {
        return // Encoded value
    }
}})
```

The type argument is also provided to the decoder:

```javascript
var decoded = qs.parse('x=z', { decoder: function (str, defaultDecoder, charset, type) {
    if (type === 'key') {
        return // Decoded key
    } else if (type === 'value') {
        return // Decoded value
    }
}})
```

Examples beyond this point will be shown as though the output is not URI encoded for clarity. Please note that the return values in these cases *will* be URI encoded during real usage.

When arrays are stringified, by default they are given explicit indices:

```javascript
qs.stringify({ a: ['b', 'c', 'd'] });
// 'a[0]=b&a[1]=c&a[2]=d'
```

You may override this by setting the `indices` option to `false`:

```javascript
qs.stringify({ a: ['b', 'c', 'd'] }, { indices: false });
// 'a=b&a=c&a=d'
```

You may use the `arrayFormat` option to specify the format of the output array:

```javascript
qs.stringify({ a: ['b', 'c'] }, { arrayFormat: 'indices' })
// 'a[0]=b&a[1]=c'
qs.stringify({ a: ['b', 'c'] }, { arrayFormat: 'brackets' })
// 'a[]=b&a[]=c'
qs.stringify({ a: ['b', 'c'] }, { arrayFormat: 'repeat' })
// 'a=b&a=c'
qs.stringify({ a: ['b', 'c'] }, { arrayFormat: 'comma' })
// 'a=b,c'
```

Note: when using `arrayFormat` set to `'comma'`, you can also pass the `commaRoundTrip` option set to `true` or `false`, to append `[]` on single-item arrays, so that they can round trip through a parse.

When objects are stringified, by default they use bracket notation:

```javascript
qs.stringify({ a: { b: { c: 'd', e: 'f' } } });
// 'a[b][c]=d&a[b][e]=f'
```

You may override this to use dot notation by setting the `allowDots` option to `true`:

```javascript
qs.stringify({ a: { b: { c: 'd', e: 'f' } } }, { allowDots: true });
// 'a.b.c=d&a.b.e=f'
```

Empty strings and null values will omit the value, but the equals sign (=) remains in place:

```javascript
assert.equal(qs.stringify({ a: '' }), 'a=');
```

Key with no values (such as an empty object or array) will return nothing:

```javascript
assert.equal(qs.stringify({ a: [] }), '');
assert.equal(qs.stringify({ a: {} }), '');
assert.equal(qs.stringify({ a: [{}] }), '');
assert.equal(qs.stringify({ a: { b: []} }), '');
assert.equal(qs.stringify({ a: { b: {}} }), '');
```

Properties that are set to `undefined` will be omitted entirely:

```javascript
assert.equal(qs.stringify({ a: null, b: undefined }), 'a=');
```

The query string may optionally be prepended with a question mark:

```javascript
assert.equal(qs.stringify({ a: 'b', c: 'd' }, { addQueryPrefix: true }), '?a=b&c=d');
```

The delimiter may be overridden with stringify as well:

```javascript
assert.equal(qs.stringify({ a: 'b', c: 'd' }, { delimiter: ';' }), 'a=b;c=d');
```

If you only want to override the serialization of `Date` objects, you can provide a `serializeDate` option:

```javascript
var date = new Date(7);
assert.equal(qs.stringify({ a: date }), 'a=1970-01-01T00:00:00.007Z'.replace(/:/g, '%3A'));
assert.equal(
    qs.stringify({ a: date }, { serializeDate: function (d) { return d.getTime(); } }),
    'a=7'
);
```

You may use the `sort` option to affect the order of parameter keys:

```javascript
function alphabeticalSort(a, b) {
    return a.localeCompare(b);
}
assert.equal(qs.stringify({ a: 'c', z: 'y', b : 'f' }, { sort: alphabeticalSort }), 'a=c&b=f&z=y');
```

Finally, you can use the `filter` option to restrict which keys will be included in the stringified output.
If you pass a function, it will be called for each key to obtain the replacement value. Otherwise, if you
pass an array, it will be used to select properties and array indices for stringification:

```javascript
function filterFunc(prefix, value) {
    if (prefix == 'b') {
        // Return an `undefined` value to omit a property.
        return;
    }
    if (prefix == 'e[f]') {
        return value.getTime();
    }
    if (prefix == 'e[g][0]') {
        return value * 2;
    }
    return value;
}
qs.stringify({ a: 'b', c: 'd', e: { f: new Date(123), g: [2] } }, { filter: filterFunc });
// 'a=b&c=d&e[f]=123&e[g][0]=4'
qs.stringify({ a: 'b', c: 'd', e: 'f' }, { filter: ['a', 'e'] });
// 'a=b&e=f'
qs.stringify({ a: ['b', 'c', 'd'], e: 'f' }, { filter: ['a', 0, 2] });
// 'a[0]=b&a[2]=d'
```

You could also use `filter` to inject custom serialization for user defined types. Consider you're working with
some api that expects query strings of the format for ranges:

```
https://domain.com/endpoint?range=30...70
```

For which you model as:

```javascript
class Range {
    constructor(from, to) {
        this.from = from;
        this.to = to;
    }
}
```

You could _inject_ a custom serializer to handle values of this type:

```javascript
qs.stringify(
    {
        range: new Range(30, 70),
    },
    {
        filter: (prefix, value) => {
            if (value instanceof Range) {
                return `${value.from}...${value.to}`;
            }
            // serialize the usual way
            return value;
        },
    }
);
// range=30...70
```

### Handling of `null` values

By default, `null` values are treated like empty strings:

```javascript
var withNull = qs.stringify({ a: null, b: '' });
assert.equal(withNull, 'a=&b=');
```

Parsing does not distinguish between parameters with and without equal signs. Both are converted to empty strings.

```javascript
var equalsInsensitive = qs.parse('a&b=');
assert.deepEqual(equalsInsensitive, { a: '', b: '' });
```

To distinguish between `null` values and empty strings use the `strictNullHandling` flag. In the result string the `null`
values have no `=` sign:

```javascript
var strictNull = qs.stringify({ a: null, b: '' }, { strictNullHandling: true });
assert.equal(strictNull, 'a&b=');
```

To parse values without `=` back to `null` use the `strictNullHandling` flag:

```javascript
var parsedStrictNull = qs.parse('a&b=', { strictNullHandling: true });
assert.deepEqual(parsedStrictNull, { a: null, b: '' });
```

To completely skip rendering keys with `null` values, use the `skipNulls` flag:

```javascript
var nullsSkipped = qs.stringify({ a: 'b', c: null}, { skipNulls: true });
assert.equal(nullsSkipped, 'a=b');
```

If you're communicating with legacy systems, you can switch to `iso-8859-1`
using the `charset` option:

```javascript
var iso = qs.stringify({ æ: 'æ' }, { charset: 'iso-8859-1' });
assert.equal(iso, '%E6=%E6');
```

Characters that don't exist in `iso-8859-1` will be converted to numeric
entities, similar to what browsers do:

```javascript
var numeric = qs.stringify({ a: '☺' }, { charset: 'iso-8859-1' });
assert.equal(numeric, 'a=%26%239786%3B');
```

You can use the `charsetSentinel` option to announce the character by
including an `utf8=✓` parameter with the proper encoding if the checkmark,
similar to what Ruby on Rails and others do when submitting forms.

```javascript
var sentinel = qs.stringify({ a: '☺' }, { charsetSentinel: true });
assert.equal(sentinel, 'utf8=%E2%9C%93&a=%E2%98%BA');

var isoSentinel = qs.stringify({ a: 'æ' }, { charsetSentinel: true, charset: 'iso-8859-1' });
assert.equal(isoSentinel, 'utf8=%26%2310003%3B&a=%E6');
```

### Dealing with special character sets

By default the encoding and decoding of characters is done in `utf-8`,
and `iso-8859-1` support is also built in via the `charset` parameter.

If you wish to encode querystrings to a different character set (i.e.
[Shift JIS](https://en.wikipedia.org/wiki/Shift_JIS)) you can use the
[`qs-iconv`](https://github.com/martinheidegger/qs-iconv) library:

```javascript
var encoder = require('qs-iconv/encoder')('shift_jis');
var shiftJISEncoded = qs.stringify({ a: 'こんにちは！' }, { encoder: encoder });
assert.equal(shiftJISEncoded, 'a=%82%B1%82%F1%82%C9%82%BF%82%CD%81I');
```

This also works for decoding of query strings:

```javascript
var decoder = require('qs-iconv/decoder')('shift_jis');
var obj = qs.parse('a=%82%B1%82%F1%82%C9%82%BF%82%CD%81I', { decoder: decoder });
assert.deepEqual(obj, { a: 'こんにちは！' });
```

### RFC 3986 and RFC 1738 space encoding

RFC3986 used as default option and encodes ' ' to *%20* which is backward compatible.
In the same time, output can be stringified as per RFC1738 with ' ' equal to '+'.

```
assert.equal(qs.stringify({ a: 'b c' }), 'a=b%20c');
assert.equal(qs.stringify({ a: 'b c' }, { format : 'RFC3986' }), 'a=b%20c');
assert.equal(qs.stringify({ a: 'b c' }, { format : 'RFC1738' }), 'a=b+c');
```

## Security

Please email [@ljharb](https://github.com/ljharb) or see https://tidelift.com/security if you have a potential security vulnerability to report.

## qs for enterprise

Available as part of the Tidelift Subscription

The maintainers of qs and thousands of other packages are working with Tidelift to deliver commercial support and maintenance for the open source dependencies you use to build your applications. Save time, reduce risk, and improve code health, while paying the maintainers of the exact dependencies you use. [Learn more.](https://tidelift.com/subscription/pkg/npm-qs?utm_source=npm-qs&utm_medium=referral&utm_campaign=enterprise&utm_term=repo)

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