Parsing URL hash/fragment identifier with JavaScript

Use URLSearchParams. It's fully supported in major browsers and server-side JavaScript runtimes that implement WHATWG URL Standard. Browser coverage: https://caniuse.com/urlsearchparams.

Read a key from the current URL (assuming you are running on a browser UA):

// window.location.hash = "#any_hash_key=any_value"

const parsedHash = new URLSearchParams(
  window.location.hash.substring(1) // any_hash_key=any_value
);

console.log(parsedHash.get("any_hash_key")); // any_value

Read a key from an arbitrary URL (make sure to check for exceptions that may be thrown by URL constructor when given URL is not valid):

const url = new URL("https://example.com#foo=bar&baz=qux&val=val+has+spaces");

const parsedHash = new URLSearchParams(
  url.hash.substring(1) // foo=bar&baz=qux&val=val+has+spaces
);

console.log(parsedHash.get("baz")); // qux
console.log(parsedHash.get("val")); // val has spaces

Check out the Mozilla docs I linked above to see all of the methods of the interface.

Here it is, modified from this query string parser:

function getHashParams() {

    var hashParams = {};
    var e,
        a = /\+/g,  // Regex for replacing addition symbol with a space
        r = /([^&;=]+)=?([^&;]*)/g,
        d = function (s) { return decodeURIComponent(s.replace(a, " ")); },
        q = window.location.hash.substring(1);

    while (e = r.exec(q))
       hashParams[d(e[1])] = d(e[2]);

    return hashParams;
}

No JQuery/plug-in required

Update:

I'm now recommending the jQuery BBQ plugin as per Hovis's answer. It covers all hash parsing issues.

Update (2019)

Apparently there is now a URLSearchParams function - see answer from @Berkant

Do this in pure Javascript:

var hash = window.location.hash.substr(1);

var result = hash.split('&').reduce(function (result, item) {
    var parts = item.split('=');
    result[parts[0]] = parts[1];
    return result;
}, {});

http://example.com/#from=2012-01-05&to=2013-01-01

becomes

{from: '2012-01-05', to:'2013-01-01'}

I am using jQuery URL Parser library.

I was looking through a bunch of answers for this problem and wound up cobbling them together using one line with reduce:

const hashObj = location.hash.replace('#', '').split('&').reduce((prev, item) => Object.assign({[item.split('=')[0]]: item.split('=')[1]}, prev), {});

There's obviously a lot going on in that one line. It can be rewritten like this for clariry:

const hashObj = location.hash.replace('#', '').split('&').reduce((prev, item) => {
  return Object.assign({[item.split('=')[0]]: item.split('=')[1]}, prev);
}, {});

My answer to this question should do what you're looking for:

url_args_decode = function (url) {
  var args_enc, el, i, nameval, ret;
  ret = {};
  // use the DOM to parse the URL via an 'a' element
  el = document.createElement("a");
  el.href = url;
  // strip off initial ? on search and split
  args_enc = el.search.substring(1).split('&');
  for (i = 0; i < args_enc.length; i++) {
    // convert + into space, split on =, and then decode 
    args_enc[i].replace(/\+/g, ' ');
    nameval = args_enc[i].split('=', 2);
    ret[decodeURIComponent(nameval[0])]=decodeURIComponent(nameval[1]);
  }
  return ret;
};

You can also use the .hash property, demonstrated in this scrolling table of contents example for a clicked link or for the locatioin.

This jquery API does parse hash tags: https://jhash.codeplex.com/

// get the "name" querystring value
var n = jHash.val('name');

// get the "location" querystring value
var l = jHash.val('location');

// set some querystring values
jHash.val({
    name: 'Chris',
    location: 'WI'
});