overlayscrollbars

What is overlayscrollbars?

OverlayScrollbars is a customizable scrollbar library for web applications. It allows developers to create custom scrollbars that can be styled and configured to match the design of their application. The library provides a variety of features including auto-hide scrollbars, native scrolling behavior, and support for both vertical and horizontal scrollbars.

What are overlayscrollbars's main functionalities?

Custom Scrollbars

This feature allows you to replace the default browser scrollbars with custom scrollbars. The code sample demonstrates how to apply OverlayScrollbars to the entire body of the document.

const OverlayScrollbars = require('overlayscrollbars');
OverlayScrollbars(document.querySelectorAll('body'), {});

Auto-Hide Scrollbars

This feature enables the scrollbars to automatically hide when not in use. The code sample shows how to configure OverlayScrollbars to auto-hide the scrollbars when the user is not scrolling.

const OverlayScrollbars = require('overlayscrollbars');
OverlayScrollbars(document.querySelectorAll('body'), { autoHide: 'scroll' });

Custom Styling

This feature allows you to apply custom styles to the scrollbars. The code sample demonstrates how to apply a dark theme to the scrollbars using a predefined class.

const OverlayScrollbars = require('overlayscrollbars');
OverlayScrollbars(document.querySelectorAll('body'), { className: 'os-theme-dark' });

Other packages similar to overlayscrollbars

simplebar

SimpleBar is a custom scrollbar library that aims to provide a simple and lightweight solution for custom scrollbars. It offers similar functionality to OverlayScrollbars, such as auto-hide scrollbars and custom styling. However, SimpleBar is designed to be more lightweight and easier to integrate.

perfect-scrollbar

Perfect Scrollbar is another library for creating custom scrollbars. It provides a minimalistic approach to custom scrollbars with a focus on performance and simplicity. Compared to OverlayScrollbars, Perfect Scrollbar offers fewer customization options but is easier to set up and use.

malihu-custom-scrollbar-plugin

Malihu Custom Scrollbar Plugin is a jQuery plugin for creating custom scrollbars. It offers a wide range of customization options and supports both vertical and horizontal scrollbars. While it provides similar functionality to OverlayScrollbars, it requires jQuery as a dependency, which may not be suitable for all projects.

README

Website   •   Examples

OverlayScrollbars

OverlayScrollbars is a javascript scrollbar plugin that hides native scrollbars, provides custom styleable overlay scrollbars and keeps the native functionality and feeling.

Why

I created this plugin because I hate ugly and space consuming scrollbars. Similar plugins haven't met my requirements in terms of features, quality, simplicity, license or browser support.

Goals & Features

• Simple, powerful and well documented API
• High browser compatibility - Firefox 59+, Chrome 55+, Opera 42+, Edge 12+, Safari 10+ and IE 11
• Can be run on the server - SSR, SSG and ISR support
• Tested on various devices - Mobile, Desktop and Tablet
• Tested with various (and mixed) inputs - Mouse, Touch and Pen
• Treeshaking - bundle only what you really need
• Automatic update detection - no polling
• Usage of latest browser features - best performance in new browsers
• Bidirectional - LTR or RTL direction support
• Supports usage on the body element
• Supports all virtual scrolling libraries
• Simple and effective scrollbar styling
• Highly customizable
• TypeScript support - fully written in TypeScript
• Dependency free - 100% self written to ensure small size and best functionality
• High quality and fully typed framework versions for react, vue, angular, svelte and solid.

Choose your framework

Additionally to the vanilla JavaScript version you can use the official framework components & utilities:

Getting started

npm & nodejs

OverlayScrollbars can be downloaded from npm or the package manager of your choice:

npm install overlayscrollbars

After installation it can be imported:

import 'overlayscrollbars/overlayscrollbars.css';
import { 
  OverlayScrollbars, 
  ScrollbarsHidingPlugin, 
  SizeObserverPlugin, 
  ClickScrollPlugin 
} from 'overlayscrollbars';

Note: If the path 'overlayscrollbars/overlayscrollbars.css' is not working use 'overlayscrollbars/styles/overlayscrollbars.css' as the import path for the CSS file.

Manual download & embedding

You can use OverlayScrollbars without any bundler or package manager.
Simply download it from the Releases or use a CDN.

• Use the javascript files with the .browser extension.
• Use the javascript files with the .es5 extension if you need to support older browsers like IE11, otherwise use the .es6 files.
• For production use the javascript / stylesheet files with the .min extension.

Embedd OverlayScrollbars manually in your HTML:

<link type="text/css" href="path/to/overlayscrollbars.css" rel="stylesheet" />
<script type="text/javascript" src="path/to/overlayscrollbars.browser.es.js" defer></script>

You can then use the global variable OverlayScrollbarsGlobal to access the api similar to how you can do it in nodejs / modules:

var { 
  OverlayScrollbars, 
  ScrollbarsHidingPlugin, 
  SizeObserverPlugin, 
  ClickScrollPlugin  
} = OverlayScrollbarsGlobal;

The examples in this documentation will use the import syntax instead of the OverlayScrollbarsGlobal object. Both versions are equivalent though.

Initialization

Note: During initialization its expected that the CSS file is loaded and parsed by the browser.

You can initialize either directly with an Element or with an Object where you have more control over the initialization process.

// simple initialization with an element
const osInstance = OverlayScrollbars(document.querySelector('#myElement'), {});

Bridging initialization flickering

If you initialize OverlayScrollbars it needs a few milliseconds to create and append all the elements to the DOM. While this period the native scrollbars are still visible and are switched out after the initialization is finished. This is perceived as flickering.

To fix this behavior apply the data-overlayscrollbars-initialize attribute to the target element (and html element if the target element is body).

<!-- for the body element -->
<html data-overlayscrollbars-initialize>
  <head></head>
  <body data-overlayscrollbars-initialize></body>
</html>

<!-- for all other elements -->
<div data-overlayscrollbars-initialize>
  OverlayScrollbars is applied to this div
</div>

Initialization with an Object

This is a in depth topic. Click here to read it.

The only required field is the target field. This is the field to which the plugin is applied to.
If you use the object initialization only with the target field, the outcome is equivalent to the element initialization:

// Both initializations have the same outcome

OverlayScrollbars(document.querySelector('#myElement'), {});
OverlayScrollbars({ target: document.querySelector('#myElement') }, {});

In the initialization object you can specify how the library is handling generated elements. For example you can appoint an existing element as the viewport element. Like this the library won't generate it but take the specified element instead:

OverlayScrollbars({ 
 target: document.querySelector('#target'),
 elements: {
   viewport: document.querySelector('#viewport'),
 },
}, {});

This is very useful if you have a fixed DOM structure and don't want OverlayScrollbars to generate its own elements. Those cases arise very often when you want an other library to work together with OverlayScrollbars.

---

You can also decide to which element the scrollbars should be applied to:

OverlayScrollbars({ 
 target: document.querySelector('#target'),
 scrollbars: {
   slot: document.querySelector('#target').parentElement,
 },
}, {});

---

And last but not least you can decide when the initialization should be canceled:

OverlayScrollbars({ 
 target: document.querySelector('#target'),
 cancel: {
   nativeScrollbarsOverlaid: true,
   body: null,
 }
}, {});

In the above example the initialization is canceled when the native scrollbars are overlaid or when your target is a body element and the plugin determined that a initialization to the body element would affect native functionality like window.scrollTo.

Options

You can initialize OverlayScrollbars with an initial set of options, which can be changed at any time with the options method:

OverlayScrollbars(document.querySelector('#myElement'), {
  overflow: {
    x: 'hidden',
  },
});

Options in depth

This is a in depth topic. Click here to read it.

The default options are:

const defaultOptions = {
  paddingAbsolute: false,
  showNativeOverlaidScrollbars: false,
  update: {
    elementEvents: [['img', 'load']],
    debounce: [0, 33],
    attributes: null,
    ignoreMutation: null,
  },
  overflow: {
    x: 'scroll',
    y: 'scroll',
  },
  scrollbars: {
    theme: 'os-theme-dark',
    visibility: 'auto',
    autoHide: 'never',
    autoHideDelay: 1300,
    autoHideSuspend: false,
    dragScroll: true,
    clickScroll: false,
    pointers: ['mouse', 'touch', 'pen'],
  },
};

paddingAbsolute

type	default
boolean	false

Indicates whether the padding for the content shall be absolute.

showNativeOverlaidScrollbars

type	default
boolean	false

Indicates whether the native overlaid scrollbars shall be visible.

update.elementEvents

type	default
Array<[string, string]> | null	[['img', 'load']]

An array of tuples. The first value in the tuple is an selector and the second value are event names. The plugin will update itself if any of the elements with the specified selector will emit any specified event. The default value can be interpreted as "The plugin will update itself if any img element emits an load event."

update.debounce

type	default
[number, number] | number | null	[0, 33]

Note: If 0 is used for the timeout, requestAnimationFrame instead of setTimeout is used for the debounce.

Debounces the MutationObserver which tracks changes to the content. If a tuple is passed, the first value is the timeout and second is the max wait. If only a number is passed you specify only the timeout and there is no max wait. With null there is no debounce. Usefull to fine-tune performance.

update.attributes

type	default
string[] | null	null

Note: There is a base array of attributes that the MutationObserver always observes, even if this option is null.

An array of additional attributes that the MutationObserver should observe for the content.

update.ignoreMutation

type	default
((mutation) => any) | null	null

A function which receives a MutationRecord as an argument. If the function returns a truthy value the mutation will be ignored and the plugin won't update. Usefull to fine-tune performance.

overflow.x

type	default
string	'scroll'

Note: Valid values are: 'hidden', 'scroll', 'visible', 'visible-hidden' and 'visible-scroll'.

The overflow behavior for the horizontal (x) axis.

overflow.y

type	default
string	'scroll'

Note: Valid values are: 'hidden', 'scroll', 'visible', 'visible-hidden' and 'visible-scroll'.

The overflow behavior for the vertical (y) axis.

scrollbars.theme

type	default
string | null	'os-theme-dark'

Applies the specified theme (classname) to the scrollbars.

scrollbars.visibility

type	default
string	'auto'

Note: Valid values are: 'visible', 'hidden', and 'auto'.

The base visibility of the scrollbars.

scrollbars.autoHide

type	default
string	'never'

Note: Valid values are: 'never', 'scroll', 'leave' and 'move'.

The possibility to hide visible scrollbars automatically after a certain user action.

scrollbars.autoHideDelay

type	default
number	1300

The delay in milliseconds before the scrollbars are hidden automatically.

scrollbars.autoHideSuspend

type	default
boolean	false

Suspend the autoHide functionality until the first scroll interaction was performed.
The default value for this option is false for backwards compatibility reasons but is recommended to be true for better accessibility.

scrollbars.dragScroll

type	default
boolean	true

Indicates whether you can drag the scrollbar handles for scrolling.

scrollbars.clickScroll

type	default
boolean	false

Note: This options requires the ClickScrollPlugin to work.

Indicates whether you can click on the scrollbar track for scrolling.

scrollbars.pointers

type	default
string[] | null	['mouse', 'touch', 'pen']

The PointerTypes the plugin should react to.

TypeScript

// The options of a OverlayScrollbars instance.
export type Options = {
  // Whether the padding shall be absolute.
  paddingAbsolute: boolean;
  // Whether to show the native scrollbars. Has only an effect it the native scrollbars are overlaid.
  showNativeOverlaidScrollbars: boolean;
  // Customizes the automatic update behavior.
  update: {
    /**
     * The given Event(s) from the elements with the given selector(s) will trigger an update.
     * Useful for everything the MutationObserver and ResizeObserver can't detect
     * e.g.: and Images `load` event or the `transitionend` / `animationend` events.
     */
    elementEvents: Array<[elementSelector: string, eventNames: string]> | null;
    /**
     * The debounce which is used to detect content changes.
     * If a tuple is provided you can customize the `timeout` and the `maxWait` in milliseconds.
     * If a single number customizes only the `timeout`.
     *
     * If the `timeout` is `0`, a debounce still exists. (its executed via `requestAnimationFrame`).
     */
    debounce: [timeout: number, maxWait: number] | number | null;
    /**
     * HTML attributes which will trigger an update if they're changed.
     * Basic attributes like `id`, `class`, `style` etc. are always observed and doesn't have to be added explicitly.
     */
    attributes: string[] | null;
    // A function which makes it possible to ignore a content mutation or null if nothing shall be ignored.
    ignoreMutation: ((mutation: MutationRecord) => any) | null;
  };
  // Customizes the overflow behavior per axis.
  overflow: {
    // The overflow behavior of the horizontal (x) axis.
    x: OverflowBehavior;
    // The overflow behavior of the vertical (y) axis.
    y: OverflowBehavior;
  };
  // Customizes appearance of the scrollbars.
  scrollbars: {
    // The scrollbars theme. The theme value will be added as `class` to all `scrollbar` elements of the instance.
    theme: string | null;
    // The scrollbars visibility behavior.
    visibility: ScrollbarsVisibilityBehavior;
    // The scrollbars auto hide behavior.
    autoHide: ScrollbarsAutoHideBehavior;
    // The scrollbars auto hide delay in milliseconds.
    autoHideDelay: number;
    // Whether the scrollbars auto hide behavior is suspended until a scroll happened.
    autoHideSuspend: boolean;
    // Whether its possible to drag the handle of a scrollbar to scroll the viewport.
    dragScroll: boolean;
    // Whether its possible to click the track of a scrollbar to scroll the viewport.
    clickScroll: boolean;
    // An array of pointer types which shall be supported.
    pointers: string[] | null;
  };
};

Events

You can initialize OverlayScrollbars with an initial set of events, which can be managed at any time with the on and off methods:

OverlayScrollbars(document.querySelector('#myElement'), {}, {
  updated(osInstance, onUpdatedArgs) {
    // ...
  }
});

Events in depth

This is a in depth topic. Click here to read it.

Note: Every event receives the instance from which it was dispatched as the first argument. Always.

initialized

arguments	description
instance	The instance which dispatched the event.

Is dispatched after all generated elements, observers and events were appended to the DOM.

updated

arguments	description
instance	The instance which dispatched the event.
onUpdatedArgs	An object which describes the update in detail.

Note: If an update was triggered but nothing changed, the event won't be dispatched.

Is dispatched after the instace was updated.

destroyed

arguments	description
instance	The instance which dispatched the event.
canceled	An boolean which indicates whether the initialization was canceled and thus destroyed.

Is dispatched after all generated elements, observers and events were removed from the DOM.

scroll

arguments	description
instance	The instance which dispatched the event.
event	The original event argument of the DOM event.

Is dispatched by scrolling the viewport.

TypeScript

// A mapping between event names and their listener arguments.
export type EventListenerArgs = {
  // Dispatched after all elements are initialized and appended.
  initialized: [instance: OverlayScrollbars];
  // Dispatched after an update.
  updated: [instance: OverlayScrollbars, onUpdatedArgs: OnUpdatedEventListenerArgs];
  // Dispatched after all elements, observers and events are destroyed.
  destroyed: [instance: OverlayScrollbars, canceled: boolean];
  // Dispatched on scroll.
  scroll: [instance: OverlayScrollbars, event: Event];
};

export interface OnUpdatedEventListenerArgs {
  // Hints which describe what changed in the DOM.
  updateHints: {
    // Whether the size of the host element changed.
    sizeChanged: boolean;
    // Whether the direction of the host element changed.
    directionChanged: boolean;
    // Whether the intrinsic height behavior changed.
    heightIntrinsicChanged: boolean;
    // Whether the overflow edge (clientWidth / clientHeight) of the viewport element changed.
    overflowEdgeChanged: boolean;
    // Whether the overflow amount changed.
    overflowAmountChanged: boolean;
    // Whether the overflow style changed.
    overflowStyleChanged: boolean;
    // Whether an host mutation took place.
    hostMutation: boolean;
    // Whether an content mutation took place.
    contentMutation: boolean;
  };
  // The changed options.
  changedOptions: PartialOptions;
  // Whether the update happened with an force invalidated cache.
  force: boolean;
}

Instance

The OverlayScrollbars instance is created by calling the OverlayScrollbars function with an element and options object.

const osInstance = OverlayScrollbars(document.body, {});

Instance Methods

This is a in depth topic. Click here to read it.

options(): Options

Get the current options of the instance.

returns	description
Options	The current options.

options(newOptions, pure?): Options

Sets the current options of the instance.

parameter	type	description
newOptions	PartialOptions	The new (partial) options which should be applied.
pure	boolean / undefined	Whether the options should be reset before the new options are added.

returns	description
Options	The complete new options.

on(eventListeners, pure?): Function

Adds event listeners to the instance.

parameter	type	description
eventListeners	EventListeners	An object which contains the added listeners. The fields are the event names and the values the listeners.
pure	boolean / undefined	Whether all already added event listeners should be removed before the new listeners are added.

returns	description
Function	A function which removes all added event listeners.

on(name, listener): Function

Adds a single event listener to the instance.

parameter	type	description
name	string	The event name.
listener	Function	The function which is invoked when the event is dispatched.

returns	description
Function	A function which removes the added event listener.

on(name, listeners): Function

Adds multiple event listeners to the instance.

parameter	type	description
name	string	The event name.
listeners	Function[]	The functions which are invoked when the event is dispatched.

returns	description
Function	A function which removes the added event listeners.

off(name, listener): void

Removes a single event listener from the instance.

parameter	type	description
name	string	The event name.
listener	Function	The function to be removed.

off(name, listeners): void

Removes multiple event listeners from the instance.

parameter	type	description
name	string	The event name.
listeners	Function[]	The functions to be removed.

update(force?): boolean

Updates the instance.

parameter	type	description
force	boolean / undefined	Whether the update should force the cache to be invalidated.

returns	description
Function	A boolean which indicates whether the update event was triggered through this update.

state(): State

Gets the instances state.

returns	description
State	An object which describes the state of the instance.

elements(): Elements

Gets the instances elments.

returns	description
Elements	An object which describes the elements of the instance.

destroy(): void

Destroys the instance and removes all added elements.

plugin(plugin: object): object | undefined

Gets the instance modules instance of the passed plugin.

returns	description
object / undefined	An object which describes the plugins instance modules instance or undefined if no instance was found.

TypeScript

// A simplified version of the OverlayScrollbars TypeScript interface.
interface OverlayScrollbars {
  // Get the current options of the instance.
  options(): Options;
  // Sets the current options of the instance.
  options(newOptions: PartialOptions, pure?: boolean): Options;

  // Adds event listeners to the instance.
  on(eventListeners: EventListeners, pure?: boolean): () => void;
  // Adds a single event listener to the instance.
  on<N extends keyof EventListenerArgs>(name: N, listener: EventListener<N>): () => void;
  // Adds multiple event listeners to the instance.
  on<N extends keyof EventListenerArgs>(name: N, listener: EventListener<N>[]): () => void;

  // Removes a single event listener from the instance.
  off<N extends keyof EventListenerArgs>(name: N, listener: EventListener<N>): void;
  // Removes multiple event listeners from the instance.
  off<N extends keyof EventListenerArgs>(name: N, listener: EventListener<N>[]): void;

  // Updates the instance.
  update(force?: boolean): boolean;

  // Gets the instances state.
  state(): State;

  // Gets the instances elements.
  elements(): Elements;

  // Destroys the instance and removes all added elements.
  destroy(): void;

  // Gets the instance modules instance of the passed plugin.
  plugin<P extends InstancePlugin>(osPlugin: P): InferInstancePluginModuleInstance<P> | undefined;
}

Static Object

The static OverlayScrollbars object.

OverlayScrollbars.plugin(SomePlugin);

Static Object Methods

This is a in depth topic. Click here to read it.

plugin(plugin): object | undefined

Adds a single plugin.

parameter	type	description
plugin	object	The plugin to be added.

returns	description
object / void	An object which describes the plugins static modules instance or void if no instance was found.

plugin(plugins): (object | void)[]

Adds multiple plugins.

parameter	type	description
plugins	object[]	The plugins to be added.

returns	description
(object / void)[]	An array which describes the plugins static modules instances or undefined if no instance was found.

valid(osInstance): boolean

Checks whether the passed value is a valid and not destroyed overlayscrollbars instance

parameter	type	description
osInstance	any	The value to be checked.

returns	description
boolean	Whether the passed value is a valid and not destroyed overlayscrollbars instance.

env(): Environment

Gets the environment.

returns	description
Environment	An object which described the environment.

TypeScript

// The OverlayScrollbars static object.
interface OverlayScrollbarsStatic {
  // Gets the instance of the passed target or `undefined` the target has no instance.
  (target: InitializationTarget): OverlayScrollbars | undefined;
  // Initializes OverlayScrollbars to the passed target with passed options and event listeners.
  (target: InitializationTarget, options: PartialOptions, eventListeners?: EventListeners): OverlayScrollbars;

  // Adds a single plugin.
  plugin(plugin: Plugin): InferStaticPluginModuleInstance<Plugin>
  // Adds multiple plugins.
  plugin(plugins: Plugin[]): InferStaticPluginModuleInstance<Plugin>[];

  // Checks whether the passed value is a valid and not destroyed overlayscrollbars instance.
  valid(osInstance: any): osInstance is OverlayScrollbars;

  // Gets the environment.
  env(): Environment;
}

Styling

OverlayScrollbars comes with two themes called os-theme-dark and os-theme-light. You can use the scrollbars.theme option to change the theme.

Custom themes can be done in multiple ways. The easiest and fastest is to use the predefined set of CSS Custom Properties aka. CSS variables. In case those aren't enought you can add custom class names or add custom styling to the existing class names.

Styling in depth

This is a in depth topic. Click here to read it.

CSS Custom properties

OverlayScrollbars provides a set of CSS Custom Properties which makes scrollbar styling easy and fast:

.os-scrollbar {
  // The size of the scrollbar
  --os-size: 0;
  // The axis-perpedicular padding of the scrollbar (horizontal: padding-y, vertical: padding-x)
  --os-padding-perpendicular: 0;
  // The axis padding of the scrollbar (horizontal: padding-x, vertical: padding-y)
  --os-padding-axis: 0;
  // The border radius of the scrollbar track
  --os-track-border-radius: 0;
  // The background of the scrollbar track
  --os-track-bg: none;
  // The :hover background of the scrollbar track
  --os-track-bg-hover: none;
  // The :active background of the scrollbar track
  --os-track-bg-active: none;
  // The border of the scrollbar track
  --os-track-border: none;
  // The :hover background of the scrollbar track
  --os-track-border-hover: none;
  // The :active background of the scrollbar track
  --os-track-border-active: none;
  // The border radius of the scrollbar handle
  --os-handle-border-radius: 0;
  // The background of the scrollbar handle
  --os-handle-bg: none;
  // The :hover background of the scrollbar handle
  --os-handle-bg-hover: none;
  // The :active background of the scrollbar handle
  --os-handle-bg-active: none;
  // The border of the scrollbar handle
  --os-handle-border: none;
  // The :hover border of the scrollbar handle
  --os-handle-border-hover: none;
  // The :active border of the scrollbar handle
  --os-handle-border-active: none;
  // The min size of the scrollbar handle
  --os-handle-min-size: 33px;
  // The max size of the scrollbar handle
  --os-handle-max-size: none;
  // The axis-perpedicular size of the scrollbar handle (horizontal: height, vertical: width)
  --os-handle-perpendicular-size: 100%;
  // The :hover axis-perpedicular size of the scrollbar handle (horizontal: height, vertical: width)
  --os-handle-perpendicular-size-hover: 100%;
  // The :active axis-perpedicular size of the scrollbar handle (horizontal: height, vertical: width)
  --os-handle-perpendicular-size-active: 100%;
  // Increases the interactive area of the scrollbar handle.
  --os-handle-interactive-area-offset: 0;
}

You can alter the properties either for both scrollbars at once or per scrollbar axis. In the example below I've chosen os-theme-custom as the theme name:

// horizontal and vertical scrollbar are 10px 
.os-theme-custom {
  --os-size: 10px;
}

// horizontal scrollbar is 10px
.os-theme-custom.os-scrollbar-horizontal {
  --os-size: 10px;
}
// vertical scrollbar is 20px
.os-theme-custom.os-scrollbar-vertical {
  --os-size: 20px;
}

You can then use your theme by assigning it via the scrollbars.theme option:

OverlayScrollbars(document.body, {
  scrollbars: {
    theme: 'os-theme-custom'
  }
});

Since scrollbar styles are usually simple, this set of options should be enough to get your desired styling. In case you need more freedom you can create your own styles by adding styling to the base class names described in the next section.

Scrollbars structure and CSS class names

The scrollbars HTML markup looks like:

<div class="os-scrollbar os-scrollbar-horizontal">
    <div class="os-scrollbar-track">
        <div class="os-scrollbar-handle">
        </div>
    </div>
</div>
<div class="os-scrollbar os-scrollbar-vertical">
    <div class="os-scrollbar-track">
        <div class="os-scrollbar-handle">
        </div>
    </div>
</div>

The class names are simplified, in a real application the .os-scrollbar element can have additional class names which modify the appearance (mostly visibility and alignment).

Below is a list of the most important class names you will encounter:

CSS class name	description
.os-scrollbar	The root element of a scrollbar.
.os-scrollbar-rtl	Indicates a RTL direction of the host element the scrollbar belongs to.
.os-scrollbar-horizontal	The root element of a horizontal scrollbar.
.os-scrollbar-vertical	The root element of a vertical scrollbar.
.os-scrollbar-handle-interactive	Indicates that the handle inside the scrollbar is interactive (scrollbars.dragScroll is true).
.os-scrollbar-track-interactive	Indicates that the track inside the scrollbar is interactive (scrollbars.clickScroll is true).
.os-scrollbar-track	The track element. This is the track of the nested handle element. If scrollbars.clickScroll is true this is the element users can click to change the scroll offset.
.os-scrollbar-handle	The handle element. If scrollbars.dragScroll is true this is the handle users can drag to change the scroll offset.

If you create your own theme, please only use the classes listed above. All other classes are modifier classes used to change visibility, alignment and pointer-events of the scrollbars.

Gotchas

Its important that the chosen theme class name in your CSS file matches the assigned theme name in the options. If the CSS class name is .my-theme the scrollbars.theme has to be 'my-theme'.

Please be aware of your stack. css-modules for example will alter your class names to prevent naming collisions. Always double check if your CSS is really what you expect it to be.

Plugins

Everything thats considered not core functionality or old browser compatibility is exposed via a plugin. This is done because all unused plugins are treeshaken and thus won't end up in your final bundle. OverlayScrollbars comes with the following plugins:

• ScrollbarsHidingPlugin: Is needed for old browsers which aren't supporting native scrollbar styling features. You can find the list of browsers where you need this plugin here (note that even though iOS Safari >= 14 is marked as unsupported you only need this plugin for iOS < 7.1).
• SizeObserverPlugin: Is needed for old browsers which aren't supporting the ResizeObserver api. You can find the list of browsers where you need this plugin here
• ClickScrollPlugin: If you want to use the option scrollbars: { clickScroll: true }.

Consuming Plugins

Plugins are consumed like:

import { 
  OverlayScrollbars, 
  ScrollbarsHidingPlugin, 
  SizeObserverPlugin, 
  ClickScrollPlugin 
} from 'overlayscrollbars';

// single plugin
OverlayScrollbars.plugin(ScrollbarsHidingPlugin);

// multiple plugins
OverlayScrollbars.plugin([SizeObserverPlugin, ClickScrollPlugin]);

Plugins in depth

This is a in depth topic. Click here to read it.

Plugins are plain objects with a single field, the name of the field is the name of the plugin. This name is the plugins identifier and must be unique across all plugin. In case multiple plugins have the same name, the last added plugin overwrites previously added plugins.

Plugin Modules

A Plugin module is the constructor of a plugin modules instance. There are two kinds of plugin modules: static and instance. A single plugin must have one or more modules. Plugin modules can return an instance, but doesnt have to.

Static Plugin Module

The static plugin module is invoked when the plugin is added with the OverlayScrollbars.plugin function.

Example plugin with a static module:

const staticPlugin = {
  // plugin has the name `examplePlugin`
  examplePlugin: {
    // static function describes a static module and returns the module instance or void / undefined if no instance is needed
    // the `osStatic` parameter is the global `OverlayScrollbars` object
    static: (osStatic) => {
      let count = 0;
      const staticPluginModuleInstance = {
        getCount: () => count,
        increment: () => { count++ },
      }
      return staticPluginModuleInstance;
    }
  }
}

When the plugin is added with the OverlayScrollbars.plugin function, the static module instance is returned:

const staticModuleInstance = OverlayScrollbars.plugin(staticPlugin); // plugins static module is invoked
staticModuleInstance.count; // 0
staticModuleInstance.increment();
staticModuleInstance.count; // 1

Instance Plugin Module

The instance plugin module is invoked when a new OverlayScrollbars instance is created but before the initialized event is dispatched.

Example plugin with a instance module:

const instancePlugin = {
  // plugin has the name `examplePlugin`
  examplePlugin: {
    // instance function describes a instance module and returns the module instance or void / undefined if no instance is needed
    // the `osInstance` parameter is the OverlayScrollbar instance the plugin is bound to
    // the `event` parameter is a function which adds events to the instance which can't be removed from outside the plugin
    // the `osStatic` parameter is the gobal OverlayScrollbar object
    instance: (osInstance, event, osStatic) => {
      let count = 0;

      const instancePluginModuleInstance = {
        getCount: () => count,
        increment: () => { count++ },
      }

      // event which fires when the instance was initialized
      event('initialized', () => {
        console.log("instance initialized");
      });

      // event which fires when the viewport was scrolled
      const removeScrollEvent = event('scroll', () => {
        console.log("viewport scrolled");
        removeScrollEvent(); // removes the event after the first scroll
      });
      
      return instancePluginModuleInstance;
    }
  }
}

When the plugin is added with the OverlayScrollbars.plugin function all OverlayScrollbar instances will add the plugin automatically from that point on. Already created instances will not have the plugin. The instance modules instance is returned with the osInstance.plugin function:

OverlayScrollbars.plugin(instancePlugin); // plugin is added

const osInstance = OverlayScrollbars(document.body, {}); // plugins instance module is invoked
const instancePluginInstance = osInstance.plugin(instancePlugin);

instancePluginInstance.count; // 0
instancePluginInstance.increment();
instancePluginInstance.count; // 1

TypeScript

// Describes a OverlayScrollbar plugin.
export type Plugin<
  // the name of the plugin
  Name extends string = string,
  // the module instance type of the static module
  S extends PluginModuleInstance | void = PluginModuleInstance | void, 
  // the module instance type of the instance module
  I extends PluginModuleInstance | void = PluginModuleInstance | void 
> = {
  [pluginName in Name]: PluginModule<S, I>;
};

// Describes a OverlayScrollbar plugin which has only a static module.
export type StaticPlugin<
  Name extends string = string,
  T extends PluginModuleInstance = PluginModuleInstance
> = Plugin<Name, T, void>;

// Describes a OverlayScrollbar plugin which has only a instance module.
export type InstancePlugin<
  Name extends string = string,
  T extends PluginModuleInstance = PluginModuleInstance
> = Plugin<Name, void, T>;

// Infers the type of the static modules instance of the passed plugin.
export type InferStaticPluginModuleInstance<T extends StaticPlugin>;

// Infers the type of the instance modules instance of the passed plugin.
export type InferInstancePluginModuleInstance<T extends InstancePlugin>;

FAQ

How do I get / set the scroll position of an element I applied OverlayScrollbars to?

If you applied OverlayScrollbars to the body element you can use window.scrollX, window.scrollY, window.scroll, window.scrollTo, window.scrollBy or any other native api.

If the plugin was applied to any other element you have to get the viewport element with the instance.elements() function first. With this element you can use element.scrollTop, element.scrollLeft, element.scroll, element.scrollTo, element.scrollBy or any other native api.

const { viewport } = osInstance.elements();
const { scrollLeft, scrollTop } = viewport; // get scroll offset
viewport.scrollTo({ top: 0 }); // set scroll offset

Is it possible to limit / adjust the scrollbar handle length?

You can adjust a scrollbars handle length by setting a min-width / min-height and max-width / max-height style:

/* horizontal boundaries */
.os-scrollbar-horizontal .os-scrollbar-handle {
  min-width: 50px;
  max-width: 200px;
}
/* vertical boundaries */
.os-scrollbar-vertical .os-scrollbar-handle {
  min-height: 40px;
  max-height: 40px;
}

You can assign the same value to both properties to force the scrollbar to be always the same size.
Setting the width and height properties won't work since those are set by the plugin automatically.

Feature comparison to v1

• The scroll function is missing. Planned as a plugin. (WIP)
• Initialization to the textarea element isn't supported yet. Planned as a plugin. (WIP)

Sponsors

Thanks to BrowserStack for sponsoring open source projects and letting me test OverlayScrollbars for free.

Future Plans

• Provide plugin based support for missing features. (treeshakeable)
• Frequent updates in terms of bug-fixes and enhancements. (always use latest browser features)
• Improve tests. (unit & browser tests)

License

MIT