qs

A querystring parsing and stringifying library with some added security.


Lead Maintainer: Nathan LaFreniere

The qs module was originally created and maintained by TJ Holowaychuk.

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'