# Top Loading Bar

> The thin line at the top of the screen while a page loads: it creeps in shrinking steps, runs to the end and slips off to the right. Starts by itself on the site's links.

Feedback & loading · loading, progress, navigation, page · HTML, CSS, vanilla JS · no dependencies · updated 2026-10-16
Demo: https://kodza.dev/components/top-loading-bar/

## Files

The code below, served as files: byte for byte what the Kodza site copies (the CSS includes its theme guard).

- [`kodza-top-loading-bar.css`](https://kodza.dev/registry/top-loading-bar/kodza-top-loading-bar.css) · 2.3 KB
- [`kodza-top-loading-bar.js`](https://kodza.dev/registry/top-loading-bar/kodza-top-loading-bar.js) · 4.8 KB
- [`kodza-top-loading-bar.html`](https://kodza.dev/registry/top-loading-bar/kodza-top-loading-bar.html) · 0.1 KB · the markup, to adapt and paste into your page

**Can you run shell commands? Download the CSS and the JS, don't retype them.** Retyping costs thousands of tokens and can drop or change lines of the CSS. Put the files where your stack expects them (Use it says where: change the `-o` paths):

```bash
curl -fsSL --create-dirs -o kodza/kodza-top-loading-bar.css https://kodza.dev/registry/top-loading-bar/kodza-top-loading-bar.css
curl -fsSL --create-dirs -o kodza/kodza-top-loading-bar.js https://kodza.dev/registry/top-loading-bar/kodza-top-loading-bar.js
```

Then load the files from your page as Use it shows, instead of pasting the content. The HTML is the part you adapt (text, links, modifiers): paste it from the Code section. Copy the CSS and the JS from the Code section only if you can't run commands, exactly as they are. (Windows PowerShell: `curl.exe`.)

## API

- Root: `.kodza-loading-bar`
- Variables (set them on the root element itself: it declares its own defaults):
  - `--kz-loadbar-color: #0a0a0a`
  - `--kz-loadbar-height: 3px`
  - `--kz-loadbar-ease: cubic-bezier(0.22, 1, 0.36, 1)`
- Attributes:
  - `data-links`
- Hooks on the root element: `root.kodzaLoadingBar` (see the comment at the top of the JS)
- Lifecycle: `kodza:init` / `kodza:destroy` on `document`, with `{ detail: { root } }` to target a container.

## Dark mode

The values Kodza uses on a dark background (`#0a0a0a`). For a page that follows the system theme, add them after the component's CSS:

```css
@media (prefers-color-scheme: dark) {
  .kodza-loading-bar {
    --kz-loadbar-color: #f2f2f0;
  }
}
```

A site with its own theme switch puts the same rules under its dark selector instead (`[data-theme="dark"] .kodza-loading-bar { … }`); a single dark section, under that section's class.

## Use it

### Plain HTML page

- CSS: `kodza/kodza-top-loading-bar.css` next to the page (the Files commands as they are), linked in `<head>`: `<link rel="stylesheet" href="kodza/kodza-top-loading-bar.css">`. Without a shell, paste it in a `<style>` in `<head>` instead. It only touches `kodza-` classes.
- HTML: where the component goes. Paste it as many times as you need: instances never interfere.
- JS: `kodza/kodza-top-loading-bar.js`, loaded with `<script src="kodza/kodza-top-loading-bar.js" defer></script>` in `<head>`. Without a shell, paste it in a `<script>` before `</body>` (or in `<head>`: it waits for the page). One copy per page, whatever the number of instances.
- Restyle with the `--kz-…` variables, set on the component's root element itself (the root declares its own defaults, so a value on an ancestor is ignored), and with the modifiers / attributes listed under API.
- Font: it takes the page's own. The Kodza look is Geist: `<link rel="stylesheet" href="https://fonts.googleapis.com/css2?family=Geist:wght@400;500;600;700&family=Geist+Mono:wght@400;500&display=swap">`.
- Content added later (AJAX navigation, a SPA route, a builder preview): start it with `document.dispatchEvent(new CustomEvent('kodza:init', { detail: { root: container } }))`; before removing it, the same call with `'kodza:destroy'` stops it and puts the original markup back.

### Claude artifact (claude.ai)

- Paste the CSS in a `<style>` and the JS in a `<script>` at the end, in the artifact itself: it loads stylesheets only from Google Fonts and scripts only from a few CDNs, so no `<link>` or `<script src>` to Kodza.
- Writing the artifact file with a shell? Insert the downloaded files (Files) with a command instead of retyping them: a line `KODZA-CSS` alone inside the `<style>`, `KODZA-JS` inside the `<script>`, then `sed -e '/^KODZA-CSS$/{r kodza/kodza-top-loading-bar.css' -e 'd' -e '}' -e '/^KODZA-JS$/{r kodza/kodza-top-loading-bar.js' -e 'd' -e '}' page.html > artifact.html`.
- Font: load Geist from Google Fonts (allowed): `<link rel="stylesheet" href="https://fonts.googleapis.com/css2?family=Geist:wght@400;500;600;700&family=Geist+Mono:wght@400;500&display=swap">`.
- Dark mode: the viewer sets `data-theme="dark"` or `"light"` on `<html>`, or nothing when it follows the system. Write the Dark mode rules twice: inside `@media (prefers-color-scheme: dark)` with `:root:not([data-theme="light"])` in front of each selector, and with `:root[data-theme="dark"]` in front of each selector.

### WordPress

- HTML: a **Custom HTML** block (or a pattern / template part). WordPress keeps this markup as it is only for users allowed to post unfiltered HTML (Administrators; Super Admins on multisite): for anyone else it strips tags such as `<svg>`, `<input>` or `<dialog>`, so add it from the theme (a pattern or template part) instead.
- CSS and JS: the downloaded files go in the theme, under `wp-content/themes/<your-theme>/kodza/` (the child theme if there is one), enqueued from its functions.php (or a code-snippets plugin):
  ```php
  add_action('wp_enqueue_scripts', function () {
    $dir = get_stylesheet_directory() . '/kodza/';
    $uri = get_stylesheet_directory_uri() . '/kodza/';
    wp_enqueue_style('kodza-top-loading-bar', $uri . 'kodza-top-loading-bar.css', [], filemtime($dir . 'kodza-top-loading-bar.css'));
    wp_enqueue_script('kodza-top-loading-bar', $uri . 'kodza-top-loading-bar.js', [], filemtime($dir . 'kodza-top-loading-bar.js'), true);
  });
  ```
  Scoped to `kodza-` classes, the CSS never touches the theme. One copy of the JS, whatever the number of blocks.
- No access to the theme files? The CSS can also go, as it is, in **Appearance → Customize → Additional CSS** (classic theme) or **Styles → Additional CSS** in the Site Editor (block theme).
- Theme with AJAX page transitions: fire `kodza:init` on the new content after each swap (and `kodza:destroy` on the old one).
- Performance plugin (WP Rocket, LiteSpeed Cache, Perfmatters…) with **Delay JavaScript execution** turned on: add `kodza` to the scripts it must not delay. Otherwise the component waits for the visitor's first scroll, tap or mouse move, and that first click can be lost.
- Colours: by default, match the theme's palette. After the component's CSS, point these variables at the theme's colours, on the component root, Kodza's value as the fallback:
  `.kodza-loading-bar { --kz-loadbar-color: var(TEXT, #0a0a0a); }`
  TEXT, BACKGROUND and ACCENT (the colour the theme fills its own buttons with) are the theme's own colour variables — block themes (theme.json, like Twenty Twenty-Five): `--wp--preset--color--contrast`, `--wp--preset--color--base`, `--wp--preset--color--contrast` (they fill their buttons with it; their accent-1… colours are decorative); Astra: `--ast-global-color-2`, `--ast-global-color-4`, `--ast-global-color-0`; Kadence: `--global-palette3`, `--global-palette9`, `--global-palette1`; GeneratePress: `--contrast`, `--base-3`, `--accent`; Blocksy: `--theme-palette-color-4`, `--theme-palette-color-8`, `--theme-palette-color-1`. Use only these names, and only if the site really has them (the theme's CSS, or Styles → Colors): the `--wp--preset--color--black`, `--white`, `--vivid-…` that WordPress adds everywhere are not the theme's palette. Another theme, or one without these variables (Hello Elementor, OceanWP): leave the variables alone, it keeps Kodza's monochrome; same when the developer asks for monochrome or the Kodza look. Leave the translucent greys (`rgba(10, 10, 10, …)`) as they are: they suit any light background. On a dark palette, set the other variables from Dark mode too.
- WordPress turns straight quotes and `--` into typographic ones in the text of a Custom HTML block (not inside `<code>` or `<pre>`).

#### With Elementor

- HTML: an **HTML** widget (Elementor shows it to administrators only). It keeps the code exactly as pasted, straight quotes included.
- CSS and JS: as above. Elementor's Site Settings → Theme Style styles every button, field, link and image of the page, components included; the theme guard at the end of the CSS keeps the component's buttons, fields and link colours as they are.
- The Elementor editor redraws each widget after the page has loaded: without the script below, the component stays still in the editor preview (the published page works). Add it once per site, in the footer like the component's script (`kodza/elementor-editor.js`, or a code-snippets plugin):

```js
// Kodza in the Elementor editor: the editor redraws each HTML widget after the page has loaded.
// Start Kodza in what it draws, stop it in what it replaces or removes. Once per site.
window.addEventListener('elementor/frontend/init', () => {
  if (!elementorFrontend.isEditMode()) return;
  class KodzaWidget extends elementorModules.frontend.handlers.Base {
    onInit() {
      super.onInit();
      this.kodza = [...this.$element[0].children];
      document.dispatchEvent(new CustomEvent('kodza:init', { detail: { root: this.$element[0] } }));
    }
    onDestroy() {
      super.onDestroy();
      this.kodza.forEach((root) => document.dispatchEvent(new CustomEvent('kodza:destroy', { detail: { root } })));
    }
  }
  elementorFrontend.elementsHandler.attachHandler('html', KodzaWidget);
});
```

- No child theme: everything can go in the HTML widget instead, `<style>` with the CSS, the HTML, then `<script>` with the JS. It works on the page and in the editor without the script above.

### Shopify

- Files: `assets/kodza-top-loading-bar.css` and `assets/kodza-top-loading-bar.js` (the Files commands with `-o assets/…`).
- In the section: `{{ 'kodza-top-loading-bar.css' | asset_url | stylesheet_tag }}` and `<script src="{{ 'kodza-top-loading-bar.js' | asset_url }}" defer></script>`, then the HTML.
- The theme editor re-renders sections: restart them with
  `document.addEventListener('shopify:section:load', (e) => document.dispatchEvent(new CustomEvent('kodza:init', { detail: { root: e.target } })));`
  and the same with `shopify:section:unload` → `kodza:destroy`.

### React / Next.js

- Files, side by side (e.g. in `components/kodza/`): `TopLoadingBar.tsx` (below), the CSS block under Code saved as `top-loading-bar.css` and the JS block as `top-loading-bar.js`, both as they are. The HTML block is already inside the component: skip it.
- Use it: `import { TopLoadingBar } from '@/components/kodza/TopLoadingBar';` then `<TopLoadingBar />`. Props: `links` (`data-links`), `vars` (the `--kz-…` variables listed under API, e.g. `vars={{ '--kz-loadbar-color': … }}`), `className`, `style` and the other props of its `<div>` (`onClick`, `aria-…`).
- Next.js App Router: it is a Client Component already (`'use client'`). Pages Router: Next.js takes global CSS only in `pages/_app`, so move the `import './top-loading-bar.css'` line there.
- Safe under StrictMode, client-side navigation and prop changes: when a prop changes, the `key` gives React a fresh element, `kodza:destroy` stops the script on the old one and `kodza:init` starts it on the new one.

```tsx
'use client';
// Kodza — Top Loading Bar, for React. From https://kodza.dev/components/top-loading-bar/
// Kodza License: free to use, client work included. Not to resell or redistribute, ported or not: https://kodza.dev/docs/#print-license
// Next to this file: top-loading-bar.css and top-loading-bar.js, the component's CSS and JS from Kodza, as they are.
// Yours to edit: the markup is plain JSX below.
// The script changes this markup once React has rendered it (it adds layers, splits text, moves
// nodes), so React must not patch it afterwards. When a prop changes, the key gives React a fresh
// element: kodza:destroy stops the script on the old one, kodza:init starts it on the new one.
import { useRef, useEffect, type ComponentPropsWithoutRef, type ComponentRef, type CSSProperties } from 'react';
import './top-loading-bar.css';

export type TopLoadingBarProps = Omit<ComponentPropsWithoutRef<'div'>, "children" | "vars" | "links"> & {
  /** data-links on the root */
  links?: string;
  /** Settings, as CSS variables on the root */
  vars?: {
    /** default: #0a0a0a */
    "--kz-loadbar-color"?: string | number;
    /** default: 3px */
    "--kz-loadbar-height"?: string | number;
    /** default: cubic-bezier(0.22, 1, 0.36, 1) */
    "--kz-loadbar-ease"?: string | number;
  };
  className?: string;
};

export function TopLoadingBar({ links, vars, className, style, ...rest }: TopLoadingBarProps) {
  const ref = useRef<ComponentRef<'div'>>(null);
  const classes = ["kodza-loading-bar", className].filter(Boolean).join(' ');
  // Everything the markup is made of: when it changes, React gets a fresh element (see the top)
  const key = JSON.stringify([classes, links, vars, style, rest]);

  // Starts the script on this element once React has rendered it, stops it when it goes
  useEffect(() => {
    const root = ref.current;
    let live = true;
    // @ts-ignore: a plain script, no types to find
    import('./top-loading-bar.js').then(() => {
      if (live) document.dispatchEvent(new CustomEvent('kodza:init', { detail: { root } }));
    });
    return () => {
      live = false;
      document.dispatchEvent(new CustomEvent('kodza:destroy', { detail: { root } }));
    };
  }, [key]);

  return (
    <div role="progressbar" aria-label="Loading the page" key={key} {...rest} className={classes} data-links={links} style={{ ...vars, ...style } as CSSProperties} ref={ref}>
      <span className="kodza-loading-bar__fill" />
    </div>
  );
}
```

## Code

```html
<div class="kodza-loading-bar" role="progressbar" aria-label="Loading the page" data-links>
  <span class="kodza-loading-bar__fill"></span>
</div>
```

```css
/* Kodza License: free to use, client work included. Not to resell or redistribute, ported or not: https://kodza.dev/docs/#print-license */
/* Kodza — Top Loading Bar
   The thin line at the top of the screen while a page loads. It jumps in, then creeps forward
   in shorter and shorter steps (it never claims to be done); when the page is there it runs to
   the end and slips off to the right. With data-links it starts by itself when a link leads
   to another page of the site. From your code: el.kodzaLoadingBar.start() / .done() / .set(0.4).
   Everything is tuned with the --kz-loadbar-* variables. */
.kodza-loading-bar {
  --kz-loadbar-color: #0a0a0a;
  --kz-loadbar-height: 3px;
  --kz-loadbar-ease: cubic-bezier(0.22, 1, 0.36, 1);
  --kz-loadbar-p: 0;

  position: fixed;
  top: 0;
  right: 0;
  left: 0;
  z-index: 9999;
  height: var(--kz-loadbar-height);
  overflow: hidden;
  pointer-events: none;
}

.kodza-loading-bar__fill {
  position: absolute;
  inset: 0;
  background: var(--kz-loadbar-color);
  transform: translateX(calc((var(--kz-loadbar-p) - 1) * 100%));
  transition: transform 0.5s var(--kz-loadbar-ease);
}

/* Done: runs to the end, quickly */
.kodza-loading-bar.is-done .kodza-loading-bar__fill {
  transition-duration: 0.3s;
}

/* Then slips off to the right */
.kodza-loading-bar.is-leaving .kodza-loading-bar__fill {
  transform: translateX(101%);
  transition: transform 0.55s cubic-bezier(0.65, 0, 0.35, 1);
}

/* Back to the start, unseen */
.kodza-loading-bar.is-idle .kodza-loading-bar__fill {
  transition: none;
}

@media (prefers-reduced-motion: reduce) {
  .kodza-loading-bar__fill,
  .kodza-loading-bar.is-leaving .kodza-loading-bar__fill {
    transition: none;
  }
}

/* Theming example — on a dark site:
.dark-site .kodza-loading-bar {
  --kz-loadbar-color: #f2f2f0;
}
*/

/* kodza-guard 097a3e222642 — generated by Kodza, do not edit.
   Theme guard: keeps a site's own CSS (WordPress themes, Bootstrap, CSS resets…) off this
   component. :not(#_) is always true and weighs as much as an id, so these lines win over
   theme rules made of classes and tags. Customise the component through its --kz-* variables. */

/* What the browser gives, on everything the component leaves to it */

.kodza-loading-bar:not(#_),
.kodza-loading-bar__fill:not(#_) {
  box-sizing: revert;
}
```

```js
// Kodza License: free to use, client work included. Not to resell or redistribute, ported or not: https://kodza.dev/docs/#print-license
// Kodza — Top Loading Bar
// start() jumps to 8% and creeps towards 90% in shrinking steps; done() runs to 100% and
// slips the line off to the right; set(p) goes to a given point. With data-links, a click on a
// link to another page of the same site starts it (and the back button resets it).
(() => {
  const SELECTOR = '.kodza-loading-bar';
  const reduceMotion = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  // One instance. Everything it starts is tied to `signal`, so kodza:destroy stops it all
  function mount(root, signal) {
    let p = 0;
    let running = false;
    let timer = 0;

    const paint = (value) => {
      p = Math.min(1, Math.max(0, value));
      root.style.setProperty('--kz-loadbar-p', p);
      root.setAttribute('aria-valuenow', Math.round(p * 100));
    };

    // Shrinking steps: a third of what is left, then less and less
    const creep = () => {
      clearTimeout(timer);
      timer = setTimeout(() => {
        if (!running) return;
        paint(p + (0.9 - p) * (0.12 + Math.random() * 0.22));
        creep();
      }, 280 + Math.random() * 420);
    };

    const start = () => {
      clearTimeout(timer);
      root.classList.remove('is-done', 'is-leaving');
      root.classList.add('is-idle');
      paint(0);
      void root.offsetWidth;
      root.classList.remove('is-idle');
      root.setAttribute('aria-busy', 'true');
      running = true;
      paint(0.08);
      creep();
    };

    const done = () => {
      if (!running) return;
      running = false;
      clearTimeout(timer);
      root.removeAttribute('aria-busy');
      root.classList.add('is-done');
      paint(1);
      timer = setTimeout(() => {
        root.classList.add('is-leaving');
        timer = setTimeout(() => {
          root.classList.add('is-idle');
          root.classList.remove('is-done', 'is-leaving');
          paint(0);
        }, reduceMotion ? 0 : 560);
      }, reduceMotion ? 200 : 320);
    };

    root.kodzaLoadingBar = { start, done, set: (value) => (running ? paint(value) : (start(), paint(value))) };
    // Stopped mid-load: the creeping and the exit stop with it
    signal.addEventListener('abort', () => {
      clearTimeout(timer);
      running = false;
      delete root.kodzaLoadingBar;
    });
    root.classList.add('is-idle');
    paint(0);

    if (root.hasAttribute('data-links')) {
      document.addEventListener('click', (event) => {
        const link = event.target.closest?.('a[href]');
        if (!link || event.defaultPrevented || event.button !== 0 || event.metaKey || event.ctrlKey || event.shiftKey || event.altKey) return;
        if (link.target && link.target !== '_self') return;
        if (link.hasAttribute('download')) return;
        const url = new URL(link.href, location.href);
        // Another page of this site (a #section of the same page loads nothing)
        if (url.origin !== location.origin || (url.pathname === location.pathname && url.search === location.search)) return;
        start();
      }, { signal });
      window.addEventListener('pageshow', (event) => event.persisted && done(), { signal });
    }
  }

  // Kodza lifecycle, the same in every component: `kodza:init` starts the instances inside
  // event.detail.root (the whole page by default), `kodza:destroy` stops them and puts their
  // markup back. For themes and apps that swap content without a page load.
  const instances = new WeakMap();
  const find = (scope = document) => [scope, ...scope.querySelectorAll(SELECTOR)].filter((el) => el.matches?.(SELECTOR));
  const init = (scope) => find(scope).forEach((root) => {
    if (root.classList.contains('is-ready')) return; // already running, maybe from another copy of this script
    const controller = new AbortController();
    instances.set(root, { controller, html: root.innerHTML, attrs: [...root.attributes].map((a) => [a.name, a.value]) });
    mount(root, controller.signal);
    root.classList.add('is-ready');
  });
  const destroy = (scope) => find(scope).forEach((root) => {
    const instance = instances.get(root);
    if (!instance) return;
    instances.delete(root);
    instance.controller.abort();
    [...root.attributes].forEach((a) => root.removeAttribute(a.name));
    instance.attrs.forEach(([name, value]) => root.setAttribute(name, value));
    root.innerHTML = instance.html;
  });
  document.addEventListener('kodza:init', (event) => init(event.detail?.root));
  document.addEventListener('kodza:destroy', (event) => destroy(event.detail?.root));
  init();
  // Loaded in <head>, the script runs before the markup exists: once more when it is parsed
  if (document.readyState === 'loading') document.addEventListener('DOMContentLoaded', () => init(), { once: true });
})();
```

Free to use, from Kodza (https://kodza.dev).