One line QueryString parser - handles repeated parameters, initial question-mark is optional, handles null parameters, handles + in parameters, and decodes URI Components.

qsparser.js

'use strict';

/**

"One line" QueryString parser

Initial question-mark optional
Handles repeated parameters (turns into array)
Handles null parameters
Handles + sign in parameters
Decodes URI Components
If no string is passed, uses "window.location.search", if it exists
Creates a bare object (Object.create(null)) so Object properties aren't present.

*/

const assert = require('assert');

// the function
function queryStringToObject(query) {
    if (!(typeof query === 'string')) {
        if (typeof window === 'object' && typeof window.location === 'object' && typeof window.location.search === 'string') {
           return queryStringToObject(window.location.search);
        } else {
           return Object.create(null);
        }
    }

    return query.substring(query[0] == '?' ? 1 : 0)
        .split('&')
        .reduce(function (acc, cur) {
            var split = cur.split('=').map(function (val) {
                return decodeURIComponent(val.replace(/\+/g, ' '));
            });
            Array.isArray(acc[split[0]]) ? acc[split[0]].push(split[1]) : acc[split[0]] == null ? acc[split[0]] = split[1] : acc[split[0]] = [acc[split[0]], split[1]];
            return acc;
        }, Object.create(null));
}

// the tests
var query = "?id=33&id=55&asdf=%26lols%3F&null=&null2=&3=blah+blah" ;

var qs = queryStringToObject(query);

assert.deepEqual(qs,
    {
        '3': 'blah blah',
        id: ['33', '55'],
        asdf: '&lols?',
        null: '',
        null2: ''
    }
);

assert.deepEqual(Object.create(null), queryStringToObject() );

assert.deepEqual(queryStringToObject("id=3ƒƒ•£®∆3&id=55&asdf=%26lols%3F&null=&null2=&3=blah+blah"),
    {
        '3': 'blah blah',
        id: ['3ƒƒ•£®∆3', '55'],
        asdf: '&lols?',
        null: '',
        null2: ''
    }
);


console.log(qs);