# qs
A querystring parsing and stringifying library with some added security.
[](http://travis-ci.org/hapijs/qs)
Lead Maintainer: [Nathan LaFreniere](https://github.com/nlf)
The **qs** module was originally created and maintained by [TJ Holowaychuk](https://github.com/visionmedia/node-querystring).
## Usage
```javascript
var Qs = require('qs');
var obj = Qs.parse('a=c'); // { a: 'c' }
var str = Qs.stringify(obj); // 'a=c'
```
### Parsing Objects
```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
{
foo: {
bar: 'baz'
}
}
```
URI encoded strings work too:
```javascript
Qs.parse('a%5Bb%5D=c');
// { a: { b: 'c' } }
```
You can also nest your objects, like `'foo[bar][baz]=foobarbaz'`:
```javascript
{
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
{
a: {
b: {
c: {
d: {
e: {
f: {
'[g][h][i]': 'j'
}
}
}
}
}
}
}
```
This depth can be overridden by passing a `depth` option to `Qs.parse(string, [options])`:
```javascript
Qs.parse('a[b][c][d][e][f][g][h][i]=j', { depth: 1 });
// { 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
Qs.parse('a=b&c=d', { parameterLimit: 1 });
// { a: 'b' }
```
An optional delimiter can also be passed:
```javascript
Qs.parse('a=b;c=d', { delimiter: ';' });
// { a: 'b', c: 'd' }
```
Delimiters can be a regular expression too:
```javascript
Qs.parse('a=b;c=d,e=f', { delimiter: /[;,]/ });
// { a: 'b', c: 'd', e: 'f' }
```
### Parsing Arrays
**qs** can also parse arrays using a similar `[]` notation:
```javascript
Qs.parse('a[]=b&a[]=c');
// { a: ['b', 'c'] }
```
You may specify an index as well:
```javascript
Qs.parse('a[1]=c&a[0]=b');
// { 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
Qs.parse('a[1]=b&a[15]=c');
// { a: ['b', 'c'] }
```
Note that an empty string is also a value, and will be preserved:
```javascript
Qs.parse('a[]=&a[]=b');
// { a: ['', 'b'] }
Qs.parse('a[0]=b&a[1]=&a[2]=c');
// { 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:
```javascript
Qs.parse('a[100]=b');
// { a: { '100': 'b' } }
```
This limit can be overridden by passing an `arrayLimit` option:
```javascript
Qs.parse('a[1]=b', { arrayLimit: 0 });
// { a: { '1': 'b' } }
```
To disable array parsing entirely, set `arrayLimit` to `-1`.
If you mix notations, **qs** will merge the two items into an object:
```javascript
Qs.parse('a[0]=b&a[b]=c');
// { a: { '0': 'b', b: 'c' } }
```
You can also create arrays of objects:
```javascript
Qs.parse('a[][b]=c');
// { a: [{ b: 'c' }] }
```
### Stringifying
```javascript
Qs.stringify(object, [options]);
```
When stringifying, **qs** always URI encodes output. Objects are stringified as you would expect:
```javascript
Qs.stringify({ a: 'b' });
// 'a=b'
Qs.stringify({ a: { b: 'c' } });
// 'a%5Bb%5D=c'
```
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'
```
Empty strings and null values will omit the value, but the equals sign (=) remains in place:
```javascript
Qs.stringify({ a: '' });
// 'a='
```
Properties that are set to `undefined` will be omitted entirely:
```javascript
Qs.stringify({ a: null, b: undefined });
// 'a='
```
The delimiter may be overridden with stringify as well:
```javascript
Qs.stringify({ a: 'b', c: 'd' }, { delimiter: ';' });
// 'a=b;c=d'
```