The $.param( ) inverse function in JavaScript / jQuery

Question

Given the following form:

<form>
 <input name="foo" value="bar">
 <input name="hello" value="hello world">
</form>

I can use the $.param( .. ) construct to serialize the form:

$.param( $('form input') )
=> foo=bar&hello=hello+world

How can I deserialize the above String with JavaScript and get a hash back?

For example,

$.magicFunction("foo=bar&hello=hello+world")
=> {'foo' : 'bar', 'hello' : 'hello world'}

Reference: jQuery.param( obj ).

• Blixt: Hey, I'm just adding this comment so you can see the update I did to the code, in case you're using it... I'd accidentally written it so that it only replaced the first +. Now it replaces all of them!
• BrunoLM: There are plugins called QueryString. I made one but it doesn't accept parameters, it only reads from window.location.search. I remember others that accept parameters...
• alexey2baranov: refactored jquery BBQ deparam() method as NPM module without dependencies npmjs.com/package/deparam
• Andrew: alexey2baranov how about refactoring deparam() without NPM as dependency? :)

Answer 1

You should use jQuery BBQ's deparam function. It's well-tested and documented.

• Felipe Castro: If you don't want to get the whole BBQ plugin, the deparam function was extracted as a standalone plugin here: github.com/chrissrogers/jquery-deparam
• pilavdzice: Unfortunately the github page hasn't seen any updates in years, and when I tried it it does not seem compatible with the latest jQuery... Looks like what I need though.

Answer 2

This is a slightly modified version of a function I wrote a while ago to do something similar.

var QueryStringToHash = function QueryStringToHash (query) {
 var query_string = {};
 var vars = query.split("&");
 for (var i=0;i<vars.length;i++) {
 var pair = vars[i].split("=");
 pair[0] = decodeURIComponent(pair[0]);
 pair[1] = decodeURIComponent(pair[1]);
 // If first entry with this name
 if (typeof query_string[pair[0]] === "undefined") {
 query_string[pair[0]] = pair[1];
 // If second entry with this name
 } else if (typeof query_string[pair[0]] === "string") {
 var arr = [ query_string[pair[0]], pair[1] ];
 query_string[pair[0]] = arr;
 // If third or later entry with this name
 } else {
 query_string[pair[0]].push(pair[1]);
 }
 } 
 return query_string;
};

• Robert Koritnik: Exactly what I thought with accepted answer "this won't work with arrays". Your solution works all right.

Answer 3

How about this short functional approach?

function parseParams(str) {
 return str.split('&').reduce(function (params, param) {
 var paramSplit = param.split('=').map(function (value) {
 return decodeURIComponent(value.replace(/\+/g, ' '));
 });
 params[paramSplit[0]] = paramSplit[1];
 return params;
 }, {});
}

Example:

parseParams("this=is&just=an&example") // Object {this: "is", just: "an", example: undefined}

• Michael Robinson: This should be the accepted answer, no external dependencies.
• fmquaglia: Simple, reliable and powerful solution. Respect, sir.
• Carsten Massmann: For what it does it is certainly a good solution. But it does not take care of arrays or objects being passed. The url field[][]=a&field[0][]=b&field[0][]=c gets processed as Object { field[][]: "a", field[0][]: "c" } where it should be resultobject.field[0] = Array [ "a", "b", "c" ]. This is the behaviour as expected from PHP. @JackyLi's solution does take care of that.

Answer 4

My answer:

function(query){
 var setValue = function(root, path, value){
 if(path.length > 1){
 var dir = path.shift();
 if( typeof root[dir] == 'undefined' ){
 root[dir] = path[0] == '' ? [] : {};
 }
 arguments.callee(root[dir], path, value);
 }else{
 if( root instanceof Array ){
 root.push(value);
 }else{
 root[path] = value;
 }
 }
 };
 var nvp = query.split('&');
 var data = {};
 for( var i = 0 ; i < nvp.length ; i++ ){
 var pair = nvp[i].split('=');
 var name = decodeURIComponent(pair[0]);
 var value = decodeURIComponent(pair[1]);
 var path = name.match(/(^[^\[]+)(\[.*\]$)?/);
 var first = path[1];
 if(path[2]){
 //case of 'array[level1]' || 'array[level1][level2]'
 path = path[2].match(/(?=\[(.*)\]$)/)[1].split('][')
 }else{
 //case of 'name'
 path = [];
 }
 path.unshift(first);
 setValue(data, path, value);
 }
 return data;
}

• Pascal Lindelauf: Yes! Yes! Yes! This is the exact one I need to parse the params that are being sent by JQuery in an $.ajax call. This returns the correctly nested hashes. Thanks so much, Jacky Li!
• Carsten Massmann: The best solution so far - It behaves pretty good! But when I use JSON.stringify(geturlargs('fld[2][]=2&fld[][]=3&fld[3][]=4&fld[]=bb&fld[]=cc').fld) I get {"2":["2"],"3":["4"],"":"cc"} and not [null,null,[2],[3,4],"bb","cc"] what I would have hoped for (this is what PHP would give me).
• Andrew: This is THE correct answer and please ignore all other anwers, they do not work properly
• delinear: This answer is the only one that addressed my particular use case (where I've passed an object with nested key/values to jQuery's $.param, this properly hydrates those values upon retrieval).
• Lou K: This might need a tweak. I just noticed if query === "" this has exception at var first = path[1];, because nvp has one item in it.

Answer 5

I am using David Dorward's answer, and realized that it doesn't behave like PHP or Ruby on Rails how they parse the params:

1) a variable is only an array if it ends with [], such as ?choice[]=1&choice[]=12, not when it is ?a=1&a=2

2) when mulitple params exist with the same name, the later ones replaces the earlier ones, as on PHP servers (Ruby on Rails keep the first one and ignore the later ones), such as ?a=1&b=2&a=3

So modifying David's version, I have:

function QueryStringToHash(query) {
 if (query == '') return null;
 var hash = {};
 var vars = query.split("&");
 for (var i = 0; i < vars.length; i++) {
 var pair = vars[i].split("=");
 var k = decodeURIComponent(pair[0]);
 var v = decodeURIComponent(pair[1]);
 // If it is the first entry with this name
 if (typeof hash[k] === "undefined") {
 if (k.substr(k.length-2) != '[]') // not end with []. cannot use negative index as IE doesn't understand it
 hash[k] = v;
 else
 hash[k.substr(0, k.length-2)] = [v];
 // If subsequent entry with this name and not array
 } else if (typeof hash[k] === "string") {
 hash[k] = v; // replace it
 // If subsequent entry with this name and is array
 } else {
 hash[k.substr(0, k.length-2)].push(v);
 }
 } 
 return hash;
};

which is tested fairly thoroughly.

• adiktofsugar: The uri spec is that ?a=1&a=2 should be an array. Ruby on Rails and PHP do not follow the actual specification.
• Baptiste Pernet: The line where you append to the array should be hash[k.substr(0, k.length-2)] = [v]; and hash[k.substr(0, k.length-2)].push(v);
• Erik van Velzen: Would be nice if this could be made available through npm

Answer 6

I know this is an old thread, but maybe there is still some relevance in it?

Inspired by Jacky Li's good solution I tried a slight variation of my own with the objective to also be able to take care of arbitrary combinations of arrays and objects as input. I looked at how PHP would have done it and tried to get something "similar" going. Here is my code:

function getargs(str){
 var ret={};
 function build(urlnam,urlval,obj){ // extend the return object ...
 var i,k,o=obj, x, rx=/\[([^\]]*)\]/g, idx=[urlnam.replace(rx,'')];
 while (x=rx.exec(urlnam)) idx.push(x[1]); 
 while(true){
 k=idx.shift();
 if(k.trim()=='') {// key is empty: autoincremented index
 if (o.constructor.name=='Array') k=o.length; // for Array
 else if (o===obj ) {k=null} // for first level property name
 else {k=-1; // for Object
 for(i in o) if (+i>k) k=+i;
 k++;
 }
 }
 if(idx.length) { 
 // set up an array if the next key (idx[0]) appears to be
 // numeric or empty, otherwise set up an object:
 if (o[k]==null || typeof o[k]!='object') o[k]=isNaN(idx[0])?{}:[]; 
 o=o[k]; // move on to the next level
 }
 else { // OK, time to store the urlval in its chosen place ...
 // console.log('key',k,'val',urlval); 
 o[k]=urlval===""?null:urlval; break; // ... and leave the while loop.
 } 
 }
 return obj;
 }
 // ncnvt: is a flag that governs the conversion of
 // numeric strings into numbers
 var ncnvt=true,i,k,p,v,argarr=[],
 ar=(str||window.location.search.substring(1)).split("&"),
 l=ar.length;
 for (i=0;i<l;i++) {if (ar[i]==="") continue;
 p=ar[i].split("=");k=decodeURIComponent(p[0]);
 v=p[1];v=(v!=null)?decodeURIComponent(v.replace(/\+/g,'%20')):'';
 if (ncnvt && v.trim()>"" && !isNaN(v)) v-=0;
 argarr.push([k,v]); // array: key-value-pairs of all arguments
 }
 for (i=0,l=argarr.length;i<l;i++) build(argarr[i][0],argarr[i][1],ret);
 return ret;
}

If the function is called without the str-argument it will assume window.location.search.slice(1) as input.

Some examples:

['a=1&a=2', // 1
 'x[y][0][z][]=1', // 2
 'hello=[%22world%22]&world=hello', // 3
 'a=1&a=2&&b&c=3&d=&=e&', // 4
 'fld[2][]=2&fld[][]=3&fld[3][]=4&fld[]=bb&fld[]=cc', // 5
 $.param({a:[[1,2],[3,4],{aa:'one',bb:'two'},[5,6]]}), // 6
 'a[]=hi&a[]=2&a[3][]=7&a[3][]=99&a[]=13',// 7
 'a[x]=hi&a[]=2&a[3][]=7&a[3][]=99&a[]=13'// 8
].map(function(v){return JSON.stringify(getargs(v));}).join('\n')

results in

{"a":2} // 1
{"x":{"y":[{"z":[1]}]}} // 2
{"hello":"[\"world\"]","world":"hello"} // 3
{"a":2,"b":null,"c":3,"d":null,"null":"e"} // 4 = { a: 2, b: null, c: 3, d: null, null: "e" }
{"fld":[null,null,[2],[3,4],"bb","cc"]} // 5 
{"a":[[1,2],[3,4],{"aa":"one","bb":"two"},[5,6]]} // 6
{"a":["hi",2,null,[7,99],13]} // 7
{"a":{"0":2,"3":[7,99],"4":13,"x":"hi"}} // 8

Whereas Jacky Li's solution would produce the outer container for a as a plain object

{a:{"0":["1","2"],"1":["3","4"],"2":["5","6"]}} // 6: JackyLi's output

getargs() looks at the first given index for any level to determine whether this level will be an object (non-numeric index) or an array (numeric or empty), thus resulting in the output as shown in the listing bove (no. 6).

If the current object is an array then nulls get inserted wherever necessary to represent empty positions. Arrays are always consecutively numbered and 0-based).

Note, that in the example no. 8 the "autoincrement" for empty indices still works, even though we are dealing with an object now and not an array.

As far as I have tested it, my getargs() behaves pretty much identically to Chriss Roger's great jQuery $.deparam() plugin mentioned in the accepted answer. The main difference is that getargs runs without jQuery and that it does autoincrement in objects while $.deparam() will not do that:

JSON.stringify($.deparam('a[x]=hi&a[]=2&a[3][]=7&a[3][]=99&a[]=13').a);

results in

{"3":["7","99"],"x":"hi","undefined":"13"}

In $.deparam() the index [] is interpreted as an undefined instead of an autoincremented numerical index.

• Andrew: thanks for this great function. However I noticed that if you use number as key in array, e.g. like ' ?a[5][]=x ' then key is used as number when creating object and thus it creates 5 empty elements in my case. It should treat numeric key as string, and thus create object with "5" (with quotes) as key and x as value. I could force url to be ' ?a["5"][]=x ' but this is ugly...
• Carsten Massmann: @Andrew: This was a deliberate design decision on my part: As far as I remember, Jack's solution will behave more in the way you expect it. I introduced the line o[k]=isNaN(idx[0])?{}:[]; with the intention of creating an array, whenever I encounter a numeric index as the first one given for a new object. Otherwise I will make a generic object. It is up to you to modify that part of the code to better suit your needs. I. e. something like o[k]={} should do the trick.
• Andrew: thanks. P.S. you should definitely remove console.log in the middle of your function ;)
• Carsten Massmann: @Andrew: Thanks, just commented it out. Must have overlooked it when I posted the code.

Answer 7

Here's how you could create a new jQuery function:

jQuery.unparam = function (value) {
 var
 // Object that holds names => values.
 params = {},
 // Get query string pieces (separated by &)
 pieces = value.split('&'),
 // Temporary variables used in loop.
 pair, i, l;
 // Loop through query string pieces and assign params.
 for (i = 0, l = pieces.length; i < l; i++) {
 pair = pieces[i].split('=', 2);
 // Repeated parameters with the same name are overwritten. Parameters
 // with no value get set to boolean true.
 params[decodeURIComponent(pair[0])] = (pair.length == 2 ?
 decodeURIComponent(pair[1].replace(/\+/g, ' ')) : true);
 }
 return params;
};

• SolutionYogi: I don't like this function. Why should parameter with no value should get the value of 'true'? Why not null? I think this design decision can lead to very subtle bugs. Also, why not handle the situation where parameter can have multiple values instead of selecting the 'last' value? Solution posted by David is much better.
• Blixt: It is true so that one can check if (params.redirect) or similar. If you want to differ between true and other value, you would use if (params.redirect === true). A null value wouldn't help in any way that I can think of. The reason I didn't do it like David is because I value consistency over flexibility. With his method I have to check if the value is a string or an array to use its value. In my opinion, it should always be a string (the true value converts to 'true' which I think is fine), or always be an array. I chose string.
• SolutionYogi: By that account, if it was params.delete, it would be set to true and I will do something harmful. As you can see, coming up with example is easy. 'null' clearly specifies that no value exists and the decision is left to the caller what how he wants to interpret it. About multiple values, look at it this way. By eating up, you are making sure that either caller will spend time debugging why he is getting only one value OR later on come and modify the code. By returning the array upfront, caller will immediately know how to handle them. Discarding information is never good, IMHO.
• Blixt: If the URL is /abc?delete then I would expect there to be an entry for delete. I don't see how that is different? I don't even see how you can prefer the other code for this reason, because that code will set the value to the string 'undefined' which is not better. And as for multiple values it's a case of simplicity vs. flexibility. I rarely see the use of multiple values in query strings, but if you want them, always return an array with 1+ values. Never mix the return type; then you will have to spend time to debug because what was usually a string could suddenly be an array.
• seb: Thanks. I don't think there is a silver bullet. I took your code and modified it a bit, removed the boolean values, added parsing of array-parameters. ?foo[]=1&foo[]=2 => foo : ["1","2"]

Answer 8

Thanks to him http://james.padolsey.com/javascript/parsing-urls-with-the-dom/

Pretty easy :D

function params_unserialize(p){
var ret = {},
 seg = p.replace(/^\?/,'').split('&'),
 len = seg.length, i = 0, s;
for (;i<len;i++) {
 if (!seg[i]) { continue; }
 s = seg[i].split('=');
 ret[s[0]] = s[1];
}
return ret;}

• Fernando Fabreti: This do not work with select boxes with multiple options, because it only keep last selected.
• brutuscat: Sorry but I can't see what is the point you are referring to in the comment. The function referenced here is to unserialize/parse an URI with params like ?something=1&param2=value2 into an array. What do you mean with "do not work with select boxes with multiple options"?

Answer 9

This is really old question, but as i have coming - other people may coming to this post, and i want to a bit refresh this theme. Today no need to make custom solutions - there is URLSearchParams interface.

var paramsString = "q=URLUtils.searchParams&topic=api";
var searchParams = new URLSearchParams(paramsString);
//Iterate the search parameters.
for (let p of searchParams) {
 console.log(p);
}

The only one limitation i know - this feature not supported in IE / Edge.

• Lauren: Unfortunately not support by IE, as per usual, in case you need to support this browser.

Answer 10

Here's my JavaScript implementation which I use in a server-side JScript ASP Classic page (demo):

// Transforms a query string in the form x[y][0][z][]=1 into {x:{y:[{z:[1]}]}}
function parseJQueryParams(p) {
 var params = {};
 var pairs = p.split('&');
 for (var i=0; i<pairs.length; i++) {
 var pair = pairs[i].split('=');
 var indices = [];
 var name = decodeURIComponent(pair[0]),
 value = decodeURIComponent(pair[1]);
 var name = name.replace(/\[([^\]]*)\]/g, 
 function(k, idx) { indices.push(idx); return ""; });
 indices.unshift(name);
 var o = params;
 for (var j=0; j<indices.length-1; j++) {
 var idx = indices[j];
 var nextIdx = indices[j+1];
 if (!o[idx]) {
 if ((nextIdx == "") || (/^[0-9]+$/.test(nextIdx)))
 o[idx] = [];
 else
 o[idx] = {};
 }
 o = o[idx];
 }
 idx = indices[indices.length-1];
 if (idx == "") {
 o.push(value);
 }
 else {
 o[idx] = value;
 }
 }
 return params;
}

• ymakux: So far the best I found for nested arrays

Answer 11

I came up with this solution, which behaves like the .Net function HttpUtility.ParseQueryString.

In the result, the query string parameters are store in properties as lists of values, so that qsObj["param"] will be the same as calling GetValues("param") in .Net.

I hope you like it. JQuery not required.

var parseQueryString = function (querystring) {
 var qsObj = new Object();
 if (querystring) {
 var parts = querystring.replace(/\?/, "").split("&");
 var up = function (k, v) {
 var a = qsObj[k];
 if (typeof a == "undefined") {
 qsObj[k] = [v];
 }
 else if (a instanceof Array) {
 a.push(v);
 }
 };
 for (var i in parts) {
 var part = parts[i];
 var kv = part.split('=');
 if (kv.length == 1) {
 var v = decodeURIComponent(kv[0] || "");
 up(null, v);
 }
 else if (kv.length > 1) {
 var k = decodeURIComponent(kv[0] || "");
 var v = decodeURIComponent(kv[1] || "");
 up(k, v);
 }
 }
 }
 return qsObj;
};

Here is how to use it:

var qsObj = parseQueryString("a=1&a=2&&b&c=3&d=&=e&");

To preview the result in the console juste type in:

JSON.stringify(qsObj)

Output:

"{"a":["1","2"],"null":["","b",""],"c":["3"],"d":[""],"":["e"]}"

Answer 12

There's a beautiful one-liner over at CSS-Tricks (original source from Nicholas Ortenzio):

function getQueryParameters(str) {
 return (str || document.location.search).replace(/(^\?)/,'').split("&").map(function(n){return n = n.split("="),this[n[0]] = n[1],this}.bind({}))[0];
}

The really clever part is how it uses the anonymous function's this object, adding a key/value pair for each of the queries in the string. That said, there's some room for improvement. I've modified it a bit below, with the following changes:

1. Added handling of empty strings and non-string input.

2. Handled URI-encoded strings (%40->@, etc).

3. Removed the default use of document.location.search when the input was empty.

4. Changed the name, made it more readable, added comments.

function deparam(str) {
 // Uses an empty 'this' to build up the results internally
 function splitQuery(query) {
 query = query.split('=').map(decodeURIComponent);
 this[query[0]] = query[1];
 return this;
 }
 // Catch bad input
 if (!str || !(typeof str === 'string' || str instanceof String))
 return {};
 // Split the string, run splitQuery on each piece, and return 'this'
 var queries = str.replace(/(^\?)/,'').split('&');
 return queries.map(splitQuery.bind({}))[0];
}

Answer 13

use this :

// convert query string to json object
var queryString = "cat=3&sort=1&page=1";
queryString
 .split("&")
 .forEach((item) => {
 const prop = item.split("=");
 filter[prop[0]] = prop[1];
 });
console.log(queryString);

Answer 14

This is my version in Coffeescript. Also works for url like http://localhost:4567/index.html?hello=[%22world%22]&world=hello#/home

getQueryString: (url)->
 return null if typeof url isnt 'string' or url.indexOf("http") is -1
 split = url.split "?"
 return null if split.length < 2 
 path = split[1]
 hash_pos = path.indexOf "#"
 path = path[0...hash_pos] if hash_pos isnt -1
 data = path.split "&"
 ret = {}
 for d in data
 [name, val] = d.split "=" 
 name = decodeURIComponent name
 val = decodeURIComponent val
 try 
 ret[name] = JSON.parse val
 catch error
 ret[name] = val
 return ret

Answer 15

Here's a simple & compact one if you only want to quickly get the parameters from a GET request:

function httpGet() {
 var a={},b,i,q=location.search.replace(/^\?/,"").split(/\&/);
 for(i in q) if(q[i]) {b=q[i].split("=");if(b[0]) a[b[0]]=
 decodeURIComponent(b[1]).replace(/\+/g," ");} return a;
}

It converts

something?aa=1&bb=2&cc=3

into an object like

{aa:1,bb:2,cc:3}

Answer 16

Creates a serialized representation of an array or object (can be used as URL query string for AJAX requests).

<button id='param'>GET</button> 
<div id="show"></div>
<script>
 $('#param').click(function () {
 var personObj = new Object();
 personObj.firstname = "vishal"
 personObj.lastname = "pambhar";
 document.getElementById('show').innerHTML=$.param(`personObj`));
 });
</script>
output:firstname=vishal&lastname=pambhar

• L. Guthardt: Code without explainations isnt welcome. Could be please go ahead and explain your code?
• Vishal Patel: Creates a serialize representation of an array or object (can be used as URL query string for AJAX requests)
• L. Guthardt: Please add explainations directly in your answer, by editing it. Not in comments though.

Answer 17

answers could use a bit of jQuery elegance:

(function($) {
var re = /([^&=]+)=?([^&]*)/g;
var decodeRE = /\+/g; // Regex for replacing addition symbol with a space
var decode = function (str) {return decodeURIComponent( str.replace(decodeRE, " ") );};
$.parseParams = function(query) {
 var params = {}, e;
 while ( e = re.exec(query) ) {
 var k = decode( e[1] ), v = decode( e[2] );
 if (k.substring(k.length - 2) === '[]') {
 k = k.substring(0, k.length - 2);
 (params[k] || (params[k] = [])).push(v);
 }
 else params[k] = v;
 }
 return params;
};
})(jQuery);

fork at https://gist.github.com/956897

Answer 18

You can use the function .serializeArray() (Link) of jQuery itself. This function returns an array of key-value pair. Result example:

[
 { name: "id", value: "1" },
 { name: "version", value: "100" }
]

• Daniel Bang: This is not what was asked. He wants to turn a string into a hash. serializeArray takes a form and returns an array.