Parsing URL query string in JavaScript.

parse_query_string.js

// Examples:
// parseQueryString('a=1&a=2')                =>  {a: '2'}
// parseQueryString('a=1', true)              =>  {a: ['1']}
// parseQueryString('a=1&a=2', true)          =>  {a: ['1', '2']}
// parseQueryString('a[][]=1&a[][]=2', true)  =>  {'a[][]': ['1', '2']}
// parseQueryString('?a;b#c')                 =>  {'?a': '', 'b#c': ''}
function parseQueryString(query, groupByName) {
    var parsed, hasOwn, pairs, pair, name, value;

    if (typeof query != 'string') {
        throw 'Invalid input';
    }

    parsed = {};
    hasOwn = parsed.hasOwnProperty;
    query = query.replace(/\+/g, ' ');
    pairs = query.split(/[&;]/);

    for (var i = 0; i < pairs.length; i++) {
        pair = pairs[i].match(/^([^=]*)=?(.*)/);
        if (pair[1]) {
            try {
                name  = decodeURIComponent(pair[1]);
                value = decodeURIComponent(pair[2]);
            } catch(e) {
                throw 'Invaid %-encoded sequence';
            }

            if (!groupByName) {
                parsed[name] = value;
            } else if (hasOwn.call(parsed, name)) {
                parsed[name].push(value);
            } else {
                parsed[name] = [value];
            }
        }
    }
    return parsed;
}


// qUnit Tests
test("parseQueryString keyval format", function() {
    deepEqual(parseQueryString('a=1'),   {'a': '1'});
    deepEqual(parseQueryString('a='),    {'a': ''});
    deepEqual(parseQueryString('a'),     {'a': ''});
    deepEqual(parseQueryString('='),     {});
    deepEqual(parseQueryString(''),      {});
    deepEqual(parseQueryString('=1'),    {});
    deepEqual(parseQueryString('==='),   {});
    deepEqual(parseQueryString('a==1'),  {'a': '=1'});
    deepEqual(parseQueryString('a%3D1'), {'a=1' : ''});
});

test("parseQueryString pair separator", function() {
    deepEqual(parseQueryString('a=1&b=1'), {a: '1', b: '1'});
    // http://www.w3.org/TR/1999/REC-html401-19991224/appendix/notes.html#h-B.2.2
    deepEqual(parseQueryString('a=1;b=1'), {a: '1', b: '1'});
});

test("parseQueryString special characters", function() {
    deepEqual(parseQueryString('&&&=1'),          {});
    deepEqual(parseQueryString('???=1'),          {'???': '1'});
    deepEqual(parseQueryString('###=1'),          {'###': '1'});
    deepEqual(parseQueryString('a+%2B+b=1'),      {'a + b': '1'});
    deepEqual(parseQueryString("\u0020\r\n\t=1"), {"\u0020\r\n\t": '1'});
    deepEqual(parseQueryString('%C2%A9=%C2%A9'),  {'©': '©'});
    deepEqual(parseQueryString('привет=пока'),    {'привет': 'пока'});
});

test("parseQueryString lists and duplicates", function() {
    deepEqual(parseQueryString('a=1&a=2'),               {'a': '2'});
    deepEqual(parseQueryString('a=1', true),             {'a': ['1']});
    deepEqual(parseQueryString('a=1&a=2', true),         {'a': ['1', '2']});
    deepEqual(parseQueryString('a[]b=1', true),          {'a[]b': ['1']});
    deepEqual(parseQueryString('a[=1', true),            {'a[': ['1']});
    deepEqual(parseQueryString('a[]=1&a[]=1', true),     {'a[]': ['1', '1']});
    deepEqual(parseQueryString('a[][]=1&a[][]=1', true), {'a[][]': ['1', '1']});
    deepEqual(parseQueryString('a[8][0]=1&a[8][1]=1', true),
                               {'a[8][0]': ['1'], 'a[8][1]': ['1']});
});

test("parseQueryString built-in property override", function() {
    deepEqual(parseQueryString('hasOwnProperty=1'), {'hasOwnProperty': '1'});
    deepEqual(parseQueryString('toString=1'),       {'toString': '1'});
});

test("parseQueryString exceptions", function() {
    throws(function() { parseQueryString('%C2%79'); },
           'Invalid UTF-8 sequence throws an exception');
    throws(function() { parseQueryString(null); },
           'Input data is a string');
});