# rt-smooth-scroll
[](https://www.npmjs.com/package/@rethink-js/rt-smooth-scroll)
[](https://www.jsdelivr.com/package/npm/@rethink-js/rt-smooth-scroll)
[](https://opensource.org/licenses/MIT)
`rt-smooth-scroll` is a lightweight JavaScript library that seamlessly integrates the **Lenis smooth scroll engine** into your sites with:
- **Automatic Lenis loading** (no extra installs needed)
- **Zero-config defaults** (Lenis defaults, unless you override via attributes)
- Support for **multiple smooth scroll instances**
- A clean global API under `window.rtSmoothScroll`
- **Smart Scroll-To actions** with indexed selectors and dynamic offsets
- **Automatic Anchor Link Conversion** (hijack native links for smooth scrolling)
- **Scroll-To Completion Hooks** (run actions/functions after a scroll-to completes)
- Per-instance configuration via HTML attributes
- Console logs showing each instance’s final resolved config
**Lenis (GitHub):** https://github.com/darkroomengineering/lenis
---
# Table of Contents
- [1. Installation](#1-installation)
- [1.1 CDN (jsDelivr)](#11-cdn-jsdelivr)
- [1.2 npm](#12-npm)
- [2. Quick Start](#2-quick-start)
- [3. Activation Rules](#3-activation-rules)
- [4. Configuration (HTML Attributes)](#4-configuration-html-attributes)
- [5. Scroll-To Actions](#5-scroll-to-actions)
- [6. Anchor Link Conversion](#6-anchor-link-conversion)
- [7. Multiple Instances](#7-multiple-instances)
- [8. Global API](#8-global-api)
- [9. Console Logging](#9-console-logging)
- [10. Troubleshooting](#10-troubleshooting)
- [11. License](#11-license)
---
## 1. Installation
### 1.1 CDN (jsDelivr)
```html
```
### 1.2 npm
```bash
npm install @rethink-js/rt-smooth-scroll
```
Then bundle or load `dist/index.min.js` as appropriate for your build setup.
---
## 2. Quick Start
Add the script to your page. With no configuration provided, `rt-smooth-scroll` will:
- Activate itself automatically (if you didn’t explicitly opt out)
- Load Lenis from CDN
- Create a root smooth scroll instance
- Expose the global API
Example:
```html
```
> Note: If you do not set any `rt-smooth-scroll-*` config attributes, the root instance uses **Lenis defaults**.
---
## 3. Activation Rules
The library is activated when:
- The attribute `rt-smooth-scroll` exists on `` or `` **OR**
- You place one or more elements with `rt-smooth-scroll-instance`
If neither is present and no instance elements are found, it **auto-enables** itself on `` by adding `rt-smooth-scroll` (so you get a working root instance by default).
---
## 4. Configuration (HTML Attributes)
### Root Mode
Add to `` or `` to enable:
```html
```
### Global Options
Place on `` or `` to configure defaults:
```html
```
Important Lenis behavior:
- `duration` and `easing` are **useless if `lerp` is defined** (this is how Lenis works).
**Core attributes:**
| Attribute | Description |
| ----------------------------------------- | ------------------------------------------------------------ |
| `rt-smooth-scroll-duration` | Lenis `duration` (only applies when `lerp` is not used) |
| `rt-smooth-scroll-lerp` | Lenis `lerp` (0 → 1) |
| `rt-smooth-scroll-orientation` | Lenis `orientation` |
| `rt-smooth-scroll-gesture-orientation` | Lenis `gestureOrientation` |
| `rt-smooth-scroll-normalize-wheel` | Alias of Lenis `smoothWheel` (legacy naming supported) |
| `rt-smooth-scroll-smooth-wheel` | Lenis `smoothWheel` |
| `rt-smooth-scroll-wheel-multiplier` | Lenis `wheelMultiplier` |
| `rt-smooth-scroll-touch-multiplier` | Lenis `touchMultiplier` |
| `rt-smooth-scroll-sync-touch` | Lenis `syncTouch` |
| `rt-smooth-scroll-sync-touch-lerp` | Lenis `syncTouchLerp` |
| `rt-smooth-scroll-touch-inertia-exponent` | Lenis `touchInertiaExponent` |
| `rt-smooth-scroll-infinite` | Lenis `infinite` |
| `rt-smooth-scroll-auto-resize` | Lenis `autoResize` |
| `rt-smooth-scroll-overscroll` | Lenis `overscroll` |
| `rt-smooth-scroll-anchors` | Lenis `anchors` (boolean or JSON) |
| `rt-smooth-scroll-auto-toggle` | Lenis `autoToggle` |
| `rt-smooth-scroll-allow-nested-scroll` | Lenis `allowNestedScroll` |
| `rt-smooth-scroll-easing` | Named easing function (only applies when `lerp` is not used) |
| `rt-smooth-scroll-options-json` | Merge additional Lenis options via JSON |
**Easing options included:**
- `linear`
- `easeInQuad`
- `easeOutQuad`
- `easeInOutQuad`
- `easeInCubic`
- `easeOutCubic`
- `easeInOutCubic`
- `easeInOutSine`
- `easeOutExpo`
### Per-Instance Configuration
Add attributes to any scroll container:
```html
```
| Attribute | Description |
| --------------------------- | -------------------------------------------------------------- |
| `rt-smooth-scroll-instance` | Marks scroll container |
| `rt-smooth-scroll-id` | Optional instance identifier |
| `rt-smooth-scroll-content` | Selector inside container (defaults to first child if omitted) |
### Advanced Selectors (wrapper/content/eventsTarget)
You can map Lenis DOM targets using selectors:
```html
```
Or per instance:
```html
```
---
## 5. Scroll-To Actions
You can trigger a smooth scroll to any element, position, or specific instance using the `rt-smooth-scroll-to` attribute on any clickable element.
### Basic Usage
```html
```
### Indexed Selectors
You can target elements by class order (1-based index) using `.class(N)` syntax.
```html
```
### Customization Attributes
You can customize the scroll behavior for specific triggers.
| Attribute | Description |
| ---------------------------- | ------------------------------------------------------------------ |
| `rt-smooth-scroll-offset` | Offset in pixels. **Supports selectors!** (See below) |
| `rt-smooth-scroll-duration` | Override scroll duration for this action |
| `rt-smooth-scroll-immediate` | Jump instantly (true/false) |
| `rt-smooth-scroll-lock` | Lock scroll during animation |
| `rt-smooth-scroll-force` | Force scroll even if stopped |
| `rt-smooth-scroll-target-id` | **Explicitly** target a specific scroll instance ID (e.g. "panel") |
### Dynamic Element Offsets
Instead of hardcoding pixels, you can pass a selector to `rt-smooth-scroll-offset`. The library will calculate that element's `offsetHeight` and apply it as a **negative offset** (perfect for sticky headers).
```html
```
### Scroll-To Completion Hooks
When a scroll-to finishes (including the built-in correction pass for layout shifts), you can run an action/function.
**Supported hook attributes:**
- Per-trigger: `rt-smooth-scroll-on-complete`
- Global default: `rt-smooth-scroll-on-complete` on `` or ``
#### 5.1 Per-trigger completion action
Click an element after the scroll completes:
```html
Contact
```
The shorthand above treats the value as a selector and will `click()` it.
You can also be explicit:
```html
Contact
```
#### 5.2 Global default completion action
Apply to all scroll-to triggers unless they override it:
```html
```
#### 5.3 Supported completion action formats
**1) Selector-only (defaults to click)**
```html
```
**2) Typed strings**
- `click:#selector`
- `focus:#selector`
- `dispatch:event-name` (fires `CustomEvent` on `window`)
- `call:functionName` (calls `window[functionName]`)
Examples:
```html
```
When using `call:functionName`, your function receives a single object:
```js
window.afterScroll = function (ctx) {
console.log("afterScroll", ctx);
};
```
`ctx` includes:
- `lenis` (the Lenis instance used)
- `trigger` (the element that initiated the scroll)
- `target` (resolved target number/element/window)
- `value` (the raw `rt-smooth-scroll-to` string)
- `id` (the explicit `rt-smooth-scroll-target-id` if provided)
**3) JSON actions (single or array)**
This is the most robust option for multi-step actions:
```html
```
Supported JSON action types:
- `{ "type": "click", "selector": "#el" }`
- `{ "type": "focus", "selector": "#el" }`
- `{ "type": "dispatch", "name": "event-name", "detail": any }`
- `{ "type": "call", "name": "functionName", "detail": any }`
For `dispatch` and `call`, `detail` is merged into the context under `detail`.
---
## 6. Anchor Link Conversion
You can automatically convert standard `` tags (e.g., ``) into smooth scroll triggers without manually adding attributes to every link.
### Enable Conversion
Add this attribute to your `` or `` tag:
```html
```
### How it works
1. **Auto-Detection:** Finds all links pointing to a hash on the current page.
2. **Hijacking:** Converts them to use the `rt-smooth-scroll-to` logic.
3. **Clean URLs:** Removes the `href` attribute so the browser URL bar does **not** update (no `#hash` in URL), keeping your history clean.
4. **Accessibility:** Automatically restores `tabindex="0"`, `role="button"`, `cursor: pointer`, and keyboard `Enter` / `Space` key support.
### Anchor link completion hook (auto-injected)
You can automatically attach a completion hook to every converted anchor link:
```html
```
Rules:
- If a link already has `rt-smooth-scroll-on-complete`, it is not overridden.
- If `rt-smooth-scroll-anchor-links-on-complete` exists, it is copied into each converted link as `rt-smooth-scroll-on-complete`.
---
## 7. Multiple Instances
`rt-smooth-scroll` supports any number of independent Lenis instances on a page. Each instance has its own wrapper + content and can be controlled individually via API.
**Context Awareness:**
If a `rt-smooth-scroll-to` button is placed **inside** a nested scroll instance, it will automatically control that parent instance, not the root window, unless you explicitly override it with `rt-smooth-scroll-target-id`.
---
## 8. Global API
After initialization, access:
```js
window.rtSmoothScroll;
```
### Common methods:
| Method | Description |
| ------------------ | ------------------------------------------------------------------- |
| `ids()` | Array of registered instance ids |
| `get(id)` | Returns Lenis instance |
| `start(id?)` | Start scroll |
| `stop(id?)` | Stop scroll |
| `toggle(id?)` | Toggle scroll |
| `resize(id?)` | Trigger Lenis resize |
| `refreshAnchors()` | Manually re-run anchor link conversion (useful for dynamic content) |
| `destroy(id?)` | Remove instance |
**Default root Lenis instance** is also exposed as:
```js
window.lenis;
```
---
## 9. Console Logging
On startup, each instance logs:
- Instance ID
- Wrapper element
- Content element
- Final resolved options
This helps you confirm exactly what configuration is applied in the browser.
---
## 10. Troubleshooting
### Scroll feels laggy / too delayed
- **Increase** `rt-smooth-scroll-lerp` (e.g. `0.2 → 0.35`) for a snappier response.
- **Decrease** `rt-smooth-scroll-lerp` (e.g. `0.1 → 0.05`) for a smoother/heavier feel.
- Leave `rt-smooth-scroll-wheel-multiplier="1"` unless you have a strong reason to change perceived speed.
### Duration / easing doesn’t seem to do anything
Lenis treats `duration` and `easing` as **useless if `lerp` is defined**. If you want time-based behavior, ensure you’re not effectively running in lerp-mode.
### My `rt-smooth-scroll-on-complete` didn’t run
Common causes:
- The selector/function name is wrong or not available at runtime.
- Your completion hook depends on DOM that’s not yet mounted/visible.
- If you are using `call:fnName`, ensure `window.fnName` exists before the scroll completes.
- If you are using JSON, ensure it is valid JSON (double quotes, no trailing commas).
---
## 11. License
MIT License
Package: `@rethink-js/rt-smooth-scroll`
GitHub: [https://github.com/Rethink-JS/rt-smooth-scroll](https://github.com/Rethink-JS/rt-smooth-scroll)
by **Rethink JS**
[https://github.com/Rethink-JS](https://github.com/Rethink-JS)