jQuery & JavaScript

Get the hash (#fragment) of the current URL in JavaScript

jQuery & JavaScript · By the Postback Notes editorial team · Published 2026-09-12

The part of a URL after # is the fragment, often called the hash. It points to a place inside the page, and scripts use it to remember a tab or a filter. It lives only in the browser: it is never sent to the server, so ASP.NET's Request.Url cannot read it.

Reading it

// URL: https://www.example.com/help.aspx?topic=forms#validation
var hash = window.location.hash;           // "#validation" ("" if none)
var name = hash.slice(1);                  // "validation"
var decoded = decodeURIComponent(name);    // handles %20 and other escapes

// From any URL string, not just the current page:
var u = new URL("https://www.example.com/a.aspx#step-2");
console.log(u.hash);                       // "#step-2"

location.hash includes the #. Decode it before comparing, because a fragment such as #caf%C3%A9 arrives encoded.

Changing it

location.hash = "settings";                       // adds a history entry, scrolls to #settings
history.replaceState(null, "", "#settings");      // changes it without a new history entry or scrolling

Reacting to changes

function showTab() {
  var id = decodeURIComponent(location.hash.slice(1)) || "overview";
  document.querySelectorAll("[role=tabpanel]").forEach(function (p) {
    p.hidden = p.id !== id;
  });
}
window.addEventListener("hashchange", showTab);
showTab(); // also on first load

With jQuery: $(window).on("hashchange", showTab);. The event fires for links like <a href="#details">, for the back and forward buttons and for script changes through location.hash (not for history.replaceState).

The server never sees it

Browsers strip the fragment before sending the request. If the server needs the value, for example to preselect a tab after a postback, copy it into a hidden field before the form is posted:

<asp:HiddenField ID="hfTab" runat="server" />
<script>
  document.forms[0].addEventListener("submit", function () {
    document.getElementById("<%= hfTab.ClientID %>").value = location.hash.slice(1);
  });
</script>

A Response.Redirect to a URL containing #section works: the browser keeps the fragment of the redirect target. For values the server must read from the URL, use the query string instead: Read the query string in the browser.

Common uses and pitfalls

Official documentation