Convert an URL query string parameter list to a Javascript object.

queryString.js

//***************************************************************************
// Copyright 2018 Jean-Philippe Gravel, P.Eng., PSEM
//
// Permission is hereby granted, free of charge, to any person obtaining a 
// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the 
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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//***************************************************************************

// Version: 1.0.0
// Release date: 2018-11-09 
//               https://xkcd.com/1179/

let paramRegex = /[?&](?:([^?&=]+)=([^?&=]+))|[?&]([^?&=]+)/g;
let objectRegex = /([^?&=\[\]]+)\[([^?&=]+)\]/;
let arrayRegex = /^([^?&=\[\]]+)\[\]$/;
let numberRegex = /^[+-]?\d+(\.\d+)?$/;
let boolRegex = /true|false/i;

// Creates an object from the URL's query string parameters.
function queryString(url) {
    let o = {};
    let m = null;
    while (m = paramRegex.exec(url)) {
        let key = (m[1] || m[3]);
        let value = _parse(m[2] || true);
        _assign(o, key, value);
    }
    return o;
}

function _parse(value) {
    if (typeof value === "string") {
        if (numberRegex.test(value)) {
            return Number(value);
        } else if (boolRegex.test(value)) {
            return value.toLowerCase() === "true";
        }
    }
    return value;
 }

function _assign(o, key, value) {
    let arrMatch = arrayRegex.exec(key);
    if (arrMatch) {
        key = arrMatch[1];
        if (!o.hasOwnProperty(key)) {
            o[key] = [];
        }
    }
    let objMatch = objectRegex.exec(key);
    if (objMatch) {
        if (!o.hasOwnProperty(objMatch[1])) {
            o[objMatch[1]] = {};
        }
        _assign(o[objMatch[1]], objMatch[2], value);
    } else {
        if (o.hasOwnProperty(key)) {
            if(o[key] instanceof Array) {
                o[key].push(value);
            } else {
                o[key] = [o[key], value];
            }
        } else {
            o[key] = value;
        }    
    }
}

The following URL string:

"http://ddd.com?start&a=hello&b=world&middle&c=1.7276&c=2&c=3&end&exists=false&this[that]=yes&this[this]=no&this[is[deep]]=deeper"

becomes:

{
  "start": true,
  "a": "hello",
  "b": "world",
  "middle": true,
  "c": [
    1.7276,
    2,
    3
  ],
  "end": true,
  "exists": false,
  "this": {
    "that": "yes",
    "this": "no",
    "is": {
      "deep": "deeper"
    }
  }
}

The following URL string:

"http://ddd.com?arr[]=test&arr[]=cdf"

becomes:

{
  "arr": [
    "test",
    "cdf"
  ]
}