0.6.0 • Public • Published


A library for imitating operating system graphical user interfaces on the web

Specifically, Windows 98 — for now at least; it could be expanded in the future.

This library powers 98.js.org, a web-based version of Windows 98, including Paint, Notepad, Sound Recorder, and more.

See the homepage for more information.


  • Menu bars, with support for checkbox items, disabled states, and submenus

  • App windows which you can drag around, maximize, minimize, close, and resize

  • Dialog and tool window variants

  • Flying titlebar animation that guides your eyes, for maximize/minimize/restore

  • Focus containment: if you Tab or Shift+Tab within a window, it wraps around to the first/last control.

  • Button styles, including lightweight buttons, disabled buttons, and default action buttons

  • Scrollbar styles, webkit-specific (in the future there could be a custom scrollbar based on a nonintrusive scrollbar library, or styles supporting a library, where you're expected to use the library directly)

    • Procedurally rendered arrows, allowing for different scrollbar sizes
    • Inversion effect when clicking on scrollbar track
  • Themeable with Windows .theme & .themepack files at runtime!


See demos online here

See also


This library currently requires jQuery for the windowing implementation. Menu bars do not require jQuery.

(Eventually I want to have no dependencies. So far I've removed jQuery from the menu code...)


The library is not (yet) provided as a single convenient file.

You can either 1. download the repository as a ZIP file, 2. clone the repository, or 3. install the library as an npm package.

You have to include scripts for the components you want to use (MenuBar.js or $Window.js), along with stylesheets for layout, a theme, and a color scheme.

Make sure to use the compiled CSS files, not the source files.

In <head>:

<link href="os-gui/layout.css" rel="stylesheet" type="text/css">
<link href="os-gui/windows-98.css" rel="stylesheet" type="text/css">
<link href="os-gui/windows-default.css" rel="stylesheet" type="text/css">

In <head> or <body>:

<script src="os-gui/MenuBar.js"></script>

<script src="lib/jquery.js"></script> <!-- required by $Window.js -->
<script src="os-gui/$Window.js"></script>


Note: The API will likely change a lot, but I maintain a Changelog.

Panel & Inset Styles

  • .inset-deep creates a 2px inset border
  • .outset-deep creates a 2px inset border (like a button or window or menu popup)
  • .inset-shallow creates a 1px inset border
  • .outset-shallow creates a 1px outset border

Button styles

Button styles are applied to button elements globally. (And if you ever want to reset it, note that you have to get rid of the pseudo element ::after as well. @TODO: scope CSS)

Toggle Buttons

To make a toggle button, add the .toggle class to the button. Make it show as pressed with the .selected class. (@TODO: rename this .pressed)

You should use the styles together with semantic aria-pressed, aria-haspopup, and/or aria-expanded attributes as appropriate.

Default Buttons

You can show button is the default action by adding .default to the button. Note that in Windows 98, this style moves from button to button depending on the focus. A rule of thumb is that it should be on the button that will trigger with Enter.

Lightweight Buttons

You can make a lightweight button by adding .lightweight to the button. Lightweight buttons are subtle and have no border until hover.

Disabled Button States

You can disable a button by adding the standard disabled attribute to the button.

Pressed Button States

You can show a button as being pressed by adding the .pressing class to the button.
This is useful for buttons that are triggered by a keystroke.

Scrollbar styles

Scrollbar styles are applied globally, but they have a -webkit- prefix, so they'll only work in "webkit-based" browsers, generally, like Chrome, Safari, and Opera.

(Can be overridden with ::-webkit-scrollbar and related selectors (but not easily reset to the browser default, unless -webkit-appearance: scrollbar works... @TODO: scope CSS)

Selection styles

Selection styles are applied globally.

(Can be overridden with ::selection (but not easily reset to the browser default... unless with unset? @TODO: scope CSS)


Creates a menu bar component.

menus should be an object holding arrays of menu item specifications, keyed by menu button name.

Returns an object with property element, which you should then append to the DOM where you want it.

See examples in the demo code.


Closes any menus that are open.


Hotkeys like Alt will be handled at the level of the given element.

By default, the scope is window (global), for the case of a single-page application where the menu bar is at the top. If you are putting the menu bar in a window, you should call this with the window's element:


or better yet,


which takes care of the keyboard scope for you.

Note that some keyboard behavior is always handled if the menu bar has focus.

Note also for iframes, you may need to call this with $window[0], iframe.contentWindow currently, but this should be changed in the future (keyboard events should be proxied).

Event: info

Can be used to implement a status bar. A description is provided as event.detail.description when rolling over menu items that specify a description. For example:

menubar.element.addEventListener("info", (event)=> {
	statusBar.textContent = event.detail?.description || "";

Event: default-info

Signals that a status bar should be reset to blank or a default message.

menubar.element.addEventListener("default-info", (event)=> {
	statusBar.textContent = "";

	// or:
	statusBar.textContent = "For Help, click Help Topics on the Help Menu.";
	// like in MS Paint (and JS Paint)

	// or:
	statusBar.textContent = "For Help, press F1.";
	// like WordPad

	// or perhaps even:
	statusBar.innerHTML = "For Help, <a href='docs'>click here</a>";
	// Note that a link is not a common pattern, and it could only work for the default text;
	// for menu item descriptions the message in the status bar is transient, so
	// you wouldn't be able to reach it to click on it.

Menu item specification

Menu item specifications are either MENU_DIVIDER - a constant indicating a horizontal rule, or an object with the following properties:

  • item: a label for the item
  • shortcut (optional): a keyboard shortcut for the item, like "Ctrl+A"; this is not functionally implemented, you'll need to listen for the shortcut yourself!
  • action (optional): a function to execute when the item is clicked (can only specify either action or checkbox)
  • checkbox (optional): an object specifying that this item should behave as a checkbox. Property check of this object should be a function that checks if the checkbox should be checked or not and returns true for checked and false for unchecked. What a cutesy name. Property toggle should be a function that toggles the state of the option, however you're storing it; called when clicked.
  • enabled (optional): can be false to unconditionally disable the item, or a function that determines whether the item should be enabled, returning true to enable the item, false to disable.
  • submenu (optional): an array of menu item specifications to create a submenu
  • description: for implementing a status bar; an info event is emitted when rolling over the item with this description

Menu hotkeys

Menus can be navigated using the first letter of the menu item, or if you place & in front of a letter in the menu item, it will be used as the hotkey.

For menu button hotkeys, you need to press Alt, and within menu popups you must press the key directly. Alt will close the menus.

If there are multiple menu items with the same hotkey, it will cycle between them without activating them. You should try to make the hotkeys unique, including between hotkeys and first letters of menu items without defined hotkeys. (This behavior is observed in Windows 98's Explorer's Favorites menu, where you can make bookmarks that match other accelerators or menu items.)


Creates a window component that can be dragged around and such, brought to the front when clicked, and closed. Different types of windows can be created with different options. Note that focus wraps within a window's content.

Returns a jQuery object with additional methods and properties (see below, after options).

The DOM node can be accessed with $window.element, and the $Window object can be accessed from the DOM node with with element.$window.

options.title: Sets the initial window caption.

options.icons: Specifies the icon of the window at different sizes. Pass an object with keys that are sizes in pixels (or "any"), and values that are the URL of an image, or an object with srcset if you want support different pixel densities, or a DOM node if you want full control (e.g. to use an <svg> or a font icon or an emoji).

options.toolWindow: If true, the window will be a tool window, which means it will not have a minimize or maximize button, and it will be shown as always focused by default. It will also have a smaller close button in the default styles.

options.parentWindow: If specified, the window will be a child of this window. For tool windows, the focus state will be shared with the parent window.

options.maximizeButton: If set to false, the window will not have a maximize button. You cannot enable this if toolWindow is true.

options.minimizeButton: If set to false, the window will not have a minimize button. You cannot enable this if toolWindow is true.

options.closeButton: If set to false, the window will not have a close button.

options.resizable: If set to true, the window can be resized by the edges and corners.

options.outerWidth: Specifies the initial width of the window, including borders.

options.outerHeight: Specifies the initial height of the window, including title bar, menu bar, and borders.

options.innerWidth: Specifies the initial width of the window contents, excluding borders.

options.innerHeight: Specifies the initial height of the window contents, excluding title bar, menu bar, and borders

options.minOuterWidth: The minimum outer width of the window (when resizing), in pixels.

options.minOuterHeight: The minimum outer height of the window (when resizing), in pixels.

options.minInnerWidth: The minimum width of the window contents (when resizing), in pixels.

options.minInnerHeight: The minimum height of the window contents (when resizing), in pixels.

options.constrainRect(rect, x_axis, y_axis): A function that can be used to constrain the window to a particular rectangle. Takes and returns a rectangle object with x, y, width, and height properties. x_axis and y_axis define what is being dragged -1 for left and top, 1 for right and bottom, and 0 for middle. Note that the window will always be constrained to not move past the minimum width and height.

options.iframes: Contains options for controlling iframe integration. By default OS-GUI will try to enhance iframes with logic to:

  • [x] Show the window as focused when the iframe has focus (this even works for nested iframes!)
  • [x] Restore focus to controls in the iframe when refocusing the window (e.g. clicking the titlebar) (this even works for nested iframes!)
  • [ ] Propagate theme to iframes (i.e. when you drag a Windows .theme file, apply it to iframes too)
    • [x] Theme is propagated to iframes when using applyCSSProperties(cssProperties, {element, recurseIntoIframes: true})
    • [ ] @TODO: apply theme for new iframes, not just existing ones (needs a place to store the current theme)
  • [ ] @TODO: proxy mouse and keyboard events to and from the iframe, to allow for:
    • [ ] Outer window to capture and prevent keyboard events
      • Handle menu Alt+(access key) hotkeys when focus is in the iframe
      • An obvious use case is a browser app that loads arbitrary interactive content, but reserves some keyboard shortcuts for its own use. That said, if you're implementing a browser inside a browser, you can't reserve any of the keyboard shortcuts that the real browser reserves! (Maybe an electron version of 98.js.org would be able to though.)
    • [ ] Iframe to handle shortcuts when menus are focused
    • [ ] Fixing issues where dragging inside the iframe (without needing pointer capture):
      • [ ] Let the iframe to handle mouseup/pointerup events outside itself, so it knows when to end dragging.
      • [ ] Let the iframe to handle mousemove/pointermove events outside itself, so it works when dragging outside the iframe (it's ugly if it stops at the border).
      • [ ] At the start of a drag when the iframe was not previously focused, the gesture should be uninterrupted. (Does this need event proxying? Or just less nosy focus-handling (don't call focus() where not needed)? I think it currently focuses each parent browsing context before restoring focus inside the iframe, and it should really just figure out if it can focus an inner control, and IF NOT focus an outer one. And it shouldn't focus() what's already focused.)
      • [ ] When dragging over elements outside the iframe, such as an overlapped window (even with an iframe inside it), the interacted iframe should be able to handle the drag. (It just needs a .pointer-is-down iframe { pointer-events: none; } and an override on the interacted iframe. I've done it in 98.js.org, easy. In addition to mousemove/pointermove proxying.)

options.iframes.ignoreCrossOrigin: Set to true to silence cross-origin warnings for iframes within the window. Focus integration can't fully work with cross-origin iframes. There will be cases where the window is not shown as focused when clicking into the iframe, and focus can't be restored to controls within the iframe.

Returns a jQuery object with additional methods and properties:


Sets the title, or if text isn't passed, returns the current title of the window.


Closes the window.


Tries to focus something within the window, in this order of priority:

  • The last focused control within the window
  • A control with class="default"
  • If it's a tool window, the parent window
  • and otherwise the window itself (specifically $window.$content)


Removes focus from the window. If focus is outside the window, it is left unchanged.


Minimizes the window. If $window.task.$task is defined it will use that as a target for minimizing, otherwise the window will minimize to the bottom of the screen.


Maximizes the window. While maximized, the window will use position: fixed, so it will not scroll with the page.


Restores the window from minimized or maximized state. If the window is not minimized or maximized, this method does nothing.


Centers the window in the page. You should call this after the contents of the window is fully rendered, or you've set a fixed size for the window.

If you have images in the window, wait for them to load before showing and centering the window, or define a fixed size for the images.


Fits the window within the page if it's partially offscreen. (Doesn't resize the window if it's too large; it'll go off the right and bottom of the screen.)


Repositions the window so that the title bar is within the bounds of the page, so it can be dragged.


Brings the window to the front by setting its z-index to larger than any z-index yet used by the windowing system.

setDimensions({ innerWidth, innerHeight, outerWidth, outerHeight })

Sets the size of the window. Pass { innerWidth, innerHeight } to specify the size in terms of the window content, or { outerWidth, outerHeight } to specify the size including the window frame.

(This may be expanded in the future to allow setting the position as well...)


Changes the icon(s) of the window. icons is in the same format as options.icons.


Sets the size of the window's title bar icon, picking the closest size that's available.


Returns the size of the window's title bar icon.


Picks the closest icon size that's available, and returns a unique DOM node (i.e. cloned).

This can be used for representing the window in the taskbar.


Appends the menu bar to the window, and sets the keyboard scope for the menu bar's hotkeys to the window.

Can be called with null to remove the menu bar.


The minimize target (taskbar button) represents the window when minimized, and is used for animating minimize and restore. If minimizeTargetElement is null, the window will minimize to the bottom of the screen (the default).

$Button(text, action)

Creates a button in the window's content area. It automatically closes the window when clicked. There's no (good) way to prevent this, as it's intended only for dialogs.

If you need any other behavior, just create a <button> and add it to the window's content area.

Returns a jQuery object.


jQuery object.
Where you can append contents to the window.


jQuery object.
The titlebar of the window, including the title, window buttons, and possibly an icon.


jQuery object.
The title portion of the titlebar.


jQuery object.
The close button.


The DOM element that represents the window.

Event: closed

Whether the window has been closed.

Event: close

Can be used to prevent closing a window, with event.preventDefault(). Since there could be multiple listeners, and another listener could prevent closing, if you want to detect when the window is actually closed, use the closed event.

Event: closed

This event is emitted when the window is closed. It cannot be prevented.

Event: window-drag-start

Can be used to prevent dragging a window, with event.preventDefault().

Event: title-change

Can be used to update a taskbar button's label.

Event: icon-change

Can be used to update a taskbar button's icon. Use $window.getIconAtSize(size) to get an appropriate icon.


parse-theme.js contains functions for parsing and applying themes.


Parses an INI file string into CSS properties.

Automatically renders dynamic theme graphics, and includes them in the CSS properties.

applyCSSProperties(cssProperties, {element=document.documentElement, recurseIntoIframes=false})

cssProperties is an object with CSS properties and values. It can also be a CSSStyleDeclaration object.

element is the element to apply the properties to.

If recurseIntoIframes is true, then the properties will be applied to all <iframe> elements within the element as well. This only works with same-origin iframes.


Can be used to update theme graphics (scrollbar icons, etc.) for a specific section of the page. Used by the demo to show variations.

Returns CSS properties representing the rendered theme graphics.

element.style.setProperty('--scrollbar-size', '30px');
applyCSSProperties(renderThemeGraphics(getComputedStyle(element)), { element });


Exports a CSS file for a theme. Assumes that the theme graphics are already rendered. Includes a "generated file" comment.


Initializes an SVG filter that can be used to make icons appear disabled. It may not work with all icons, since it uses the black parts of the image to form a shape.

Usage from CSS:

button:disabled .icon {
	filter: saturate(0%) opacity(50%); /* fallback until SVG filter is initialized */
	filter: url("#os-gui-black-to-inset-filter");


Licensed under the MIT License, see LICENSE for details.


Install Node.js if you don't already have it.

Clone the repository, then in the project directory run npm i to install the dependencies. Also run npm i when pulling in changes from the repository, in case there are changes to the dependencies.

Run npm start to open a development server. It will open a demo page in your default browser. Changes to the library will be automatically recompiled, and the page will automatically reload.

It's a good idea to close the server when updating or installing dependencies; otherwise you may run into EPERM issues.

The styles are written with PostCSS, for mixins and other transforms.
Recommended: install a PostCSS language plugin for your editor, like PostCSS Language Support for VS Code.

Currently there's some CSS that has to manually be regenerated in-browser and copied into theme-specific CSS files.
In the future this could be done with a custom PostCSS syntax parser for .theme/.themepack files, and maybe SVG instead of any raster graphics to avoid needing node-canvas (native dependencies are a pain). Or maybe UPNG.js and plain pixel manipulation.

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