How to convert URL parameters to a JavaScript object?

One liner. Clean and simple.

const params = Object.fromEntries(new URLSearchParams(location.search));

For your specific case, it would be:

const str = 'abc=foo&def=%5Basf%5D&xyz=5';
const params = Object.fromEntries(new URLSearchParams(str));
console.log(params);

2022 One-Liner Approach

For the general case where you want to parse query params to an object:

Object.fromEntries(new URLSearchParams(location.search));

For your specific case:

Object.fromEntries(new URLSearchParams('abc=foo&def=%5Basf%5D&xyz=5'));

2022 ES6/7/8 and on approach

Starting ES6 and on, Javascript offers several constructs in order to create a performant solution for this issue.

This includes using URLSearchParams and iterators

let params = new URLSearchParams('abc=foo&def=%5Basf%5D&xyz=5');
params.get("abc"); // "foo"

Should your use case requires you to actually convert it to object, you can implement the following function:

function paramsToObject(entries) {
  const result = {}
  for(const [key, value] of entries) { // each 'entry' is a [key, value] tupple
    result[key] = value;
  }
  return result;
}

Basic Demo

const urlParams = new URLSearchParams('abc=foo&def=%5Basf%5D&xyz=5');
const entries = urlParams.entries(); //returns an iterator of decoded [key,value] tuples
const params = paramsToObject(entries); //{abc:"foo",def:"[asf]",xyz:"5"}

Using Object.fromEntries and spread

We can use Object.fromEntries, replacing paramsToObject with Object.fromEntries(entries).

The value pairs to iterate over are the list name-value pairs with the key being the name and the value being the value.

Since URLParams, returns an iterable object, using the spread operator instead of calling .entries will also yield entries per its spec:

const urlParams = new URLSearchParams('abc=foo&def=%5Basf%5D&xyz=5');
const params = Object.fromEntries(urlParams); // {abc: "foo", def: "[asf]", xyz: "5"}

Note: All values are automatically strings as per the URLSearchParams spec

Multiple same keys

As @siipe pointed out, strings containing multiple same-key values will be coerced into the last available value: foo=first_value&foo=second_value will in essence become: {foo: "second_value"}.

As per this answer: https://stackoverflow.com/a/1746566/1194694 there's no spec for deciding what to do with it and each framework can behave differently.

A common use case will be to join the two same values into an array, making the output object into:

{foo: ["first_value", "second_value"]}

This can be achieved with the following code:

const groupParamsByKey = (params) => [...params.entries()].reduce((acc, tuple) => {
 // getting the key and value from each tuple
 const [key, val] = tuple;
 if(acc.hasOwnProperty(key)) {
    // if the current key is already an array, we'll add the value to it
    if(Array.isArray(acc[key])) {
      acc[key] = [...acc[key], val]
    } else {
      // if it's not an array, but contains a value, we'll convert it into an array
      // and add the current value to it
      acc[key] = [acc[key], val];
    }
 } else {
  // plain assignment if no special case is present
  acc[key] = val;
 }

return acc;
}, {});

const params = new URLSearchParams('abc=foo&def=%5Basf%5D&xyz=5&def=dude');
const output = groupParamsByKey(params) // {abc: "foo", def: ["[asf]", "dude"], xyz: 5}

In the year 2021... Please consider this obsolete.

Edit

This edit improves and explains the answer based on the comments.

var search = location.search.substring(1);
JSON.parse('{"' + decodeURI(search).replace(/"/g, '\\"').replace(/&/g, '","').replace(/=/g,'":"') + '"}')

Example

Parse abc=foo&def=%5Basf%5D&xyz=5 in five steps:

  • decodeURI: abc=foo&def=[asf]&xyz=5
  • Escape quotes: same, as there are no quotes
  • Replace &: abc=foo","def=[asf]","xyz=5
  • Replace =: abc":"foo","def":"[asf]","xyz":"5
  • Suround with curlies and quotes: {"abc":"foo","def":"[asf]","xyz":"5"}

which is legal JSON.

An improved solution allows for more characters in the search string. It uses a reviver function for URI decoding:

var search = location.search.substring(1);
JSON.parse('{"' + search.replace(/&/g, '","').replace(/=/g,'":"') + '"}', function(key, value) { return key===""?value:decodeURIComponent(value) })

Example

search = "abc=foo&def=%5Basf%5D&xyz=5&foo=b%3Dar";

gives

Object {abc: "foo", def: "[asf]", xyz: "5", foo: "b=ar"}

Original answer

A one-liner:

JSON.parse('{"' + decodeURI("abc=foo&def=%5Basf%5D&xyz=5".replace(/&/g, "\",\"").replace(/=/g,"\":\"")) + '"}')

Tags:

Javascript

Url

Url Parameters

Url Parsing

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