# Scrollspy

Automatically update Bootstrap navigation or list group components based on scroll position to indicate which link is currently active in the viewport.

## How it works

Scrollspy has a few requirements to function properly:

- It must be used on a Bootstrap nav component or list group.
- Scrollspy requires `position: relative;` on the element you’re spying on, usually the `<body>`.
- When spying on elements other than the `<body>`, be sure to have a `height` set and `overflow-y: scroll;` applied.
- Anchors (`<a>`) are required and must point to an element with that `id`.

When successfully implemented, your nav or list group will update accordingly, moving the `.active` class from one item to the next based on their associated targets.

## Example in navbar

Scroll the area below the navbar and watch the active class change. The dropdown items will be highlighted as well.

#### @fat

Ad leggings keytar, brunch id art party dolor labore. Pitchfork yr enim lo-fi before they sold out qui. Tumblr farm-to-table bicycle rights whatever. Anim keffiyeh carles cardigan. Velit seitan mcsweeney's photo booth 3 wolf moon irure. Cosby sweater lomo jean shorts, williamsburg hoodie minim qui you probably haven't heard of them et cardigan trust fund culpa biodiesel wes anderson aesthetic. Nihil tattooed accusamus, cred irony biodiesel keffiyeh artisan ullamco consequat.

#### @mdo

Veniam marfa mustache skateboard, adipisicing fugiat velit pitchfork beard. Freegan beard aliqua cupidatat mcsweeney's vero. Cupidatat four loko nisi, ea helvetica nulla carles. Tattooed cosby sweater food truck, mcsweeney's quis non freegan vinyl. Lo-fi wes anderson +1 sartorial. Carles non aesthetic exercitation quis gentrify. Brooklyn adipisicing craft beer vice keytar deserunt.

#### one

Occaecat commodo aliqua delectus. Fap craft beer deserunt skateboard ea. Lomo bicycle rights adipisicing banh mi, velit ea sunt next level locavore single-origin coffee in magna veniam. High life id vinyl, echo park consequat quis aliquip banh mi pitchfork. Vero VHS est adipisicing. Consectetur nisi DIY minim messenger bag. Cred ex in, sustainable delectus consectetur fanny pack iphone.

#### two

In incididunt echo park, officia deserunt mcsweeney's proident master cleanse thundercats sapiente veniam. Excepteur VHS elit, proident shoreditch +1 biodiesel laborum craft beer. Single-origin coffee wayfarers irure four loko, cupidatat terry richardson master cleanse. Assumenda you probably haven't heard of them art party fanny pack, tattooed nulla cardigan tempor ad. Proident wolf nesciunt sartorial keffiyeh eu banh mi sustainable. Elit wolf voluptate, lo-fi ea portland before they sold out four loko. Locavore enim nostrud mlkshk brooklyn nesciunt.

#### three

Ad leggings keytar, brunch id art party dolor labore. Pitchfork yr enim lo-fi before they sold out qui. Tumblr farm-to-table bicycle rights whatever. Anim keffiyeh carles cardigan. Velit seitan mcsweeney's photo booth 3 wolf moon irure. Cosby sweater lomo jean shorts, williamsburg hoodie minim qui you probably haven't heard of them et cardigan trust fund culpa biodiesel wes anderson aesthetic. Nihil tattooed accusamus, cred irony biodiesel keffiyeh artisan ullamco consequat.

Keytar twee blog, culpa messenger bag marfa whatever delectus food truck. Sapiente synth id assumenda. Locavore sed helvetica cliche irony, thundercats you probably haven't heard of them consequat hoodie gluten-free lo-fi fap aliquip. Labore elit placeat before they sold out, terry richardson proident brunch nesciunt quis cosby sweater pariatur keffiyeh ut helvetica artisan. Cardigan craft beer seitan readymade velit. VHS chambray laboris tempor veniam. Anim mollit minim commodo ullamco thundercats.

                          <nav id="navbar-example2" class="navbar navbar-light bg-light px-3">
                            <a class="navbar-brand" href="#">Navbar</a>
                            <ul class="nav nav-pills">
                              <li class="nav-item">
                                <a class="nav-link" href="#fat">@fat</a>
                              </li>
                              <li class="nav-item">
                                <a class="nav-link" href="#mdo">@mdo</a>
                              </li>
                              <li class="nav-item dropdown">
                                <a class="nav-link dropdown-toggle" data-bs-toggle="dropdown" href="#" role="button" aria-expanded="false">Dropdown</a>
                                <ul class="dropdown-menu dropdown-menu-right">
                                  <li><a class="dropdown-item" href="#one">one</a></li>
                                  <li><a class="dropdown-item" href="#two">two</a></li>
                                  <li><hr class="dropdown-divider"></li>
                                  <li><a class="dropdown-item" href="#three">three</a></li>
                                </ul>
                              </li>
                            </ul>
                          </nav>
                          <div data-spy="scroll" data-bs-target="#navbar-example2" data-offset="0">
                            <h4 id="fat">@fat</h4>
                            <p>...</p>
                            <h4 id="mdo">@mdo</h4>
                            <p>...</p>
                            <h4 id="one">one</h4>
                            <p>...</p>
                            <h4 id="two">two</h4>
                            <p>...</p>
                            <h4 id="three">three</h4>
                            <p>...</p>
                          </div>

## Example with list-group

Scrollspy also works with `.list-group`s. Scroll the area next to the list group and watch the active class change.

Item 1 Item 2 Item 3 Item 4

#### Item 1

Ex consequat commodo adipisicing exercitation aute excepteur occaecat ullamco duis aliqua id magna ullamco eu. Do aute ipsum ipsum ullamco cillum consectetur ut et aute consectetur labore. Fugiat laborum incididunt tempor eu consequat enim dolore proident. Qui laborum do non excepteur nulla magna eiusmod consectetur in. Aliqua et aliqua officia quis et incididunt voluptate non anim reprehenderit adipisicing dolore ut consequat deserunt mollit dolore. Aliquip nulla enim veniam non fugiat id cupidatat nulla elit cupidatat commodo velit ut eiusmod cupidatat elit dolore.

#### Item 2

Quis magna Lorem anim amet ipsum do mollit sit cillum voluptate ex nulla tempor. Laborum consequat non elit enim exercitation cillum aliqua consequat id aliqua. Esse ex consectetur mollit voluptate est in duis laboris ad sit ipsum anim Lorem. Incididunt veniam velit elit elit veniam Lorem aliqua quis ullamco deserunt sit enim elit aliqua esse irure. Laborum nisi sit est tempor laborum mollit labore officia laborum excepteur commodo non commodo dolor excepteur commodo. Ipsum fugiat ex est consectetur ipsum commodo tempor sunt in proident.

#### Item 3

Quis anim sit do amet fugiat dolor velit sit ea ea do reprehenderit culpa duis. Nostrud aliqua ipsum fugiat minim proident occaecat excepteur aliquip culpa aute tempor reprehenderit. Deserunt tempor mollit elit ex pariatur dolore velit fugiat mollit culpa irure ullamco est ex ullamco excepteur.

#### Item 4

Quis anim sit do amet fugiat dolor velit sit ea ea do reprehenderit culpa duis. Nostrud aliqua ipsum fugiat minim proident occaecat excepteur aliquip culpa aute tempor reprehenderit. Deserunt tempor mollit elit ex pariatur dolore velit fugiat mollit culpa irure ullamco est ex ullamco excepteur.

                          <div id="list-example" class="list-group">
                            <a class="list-group-item list-group-item-action" href="#list-item-1">Item 1</a>
                            <a class="list-group-item list-group-item-action" href="#list-item-2">Item 2</a>
                            <a class="list-group-item list-group-item-action" href="#list-item-3">Item 3</a>
                            <a class="list-group-item list-group-item-action" href="#list-item-4">Item 4</a>
                          </div>
                          <div data-spy="scroll" data-bs-target="#list-example" data-offset="0" class="scrollspy-example">
                            <h4 id="list-item-1">Item 1</h4>
                            <p>...</p>
                            <h4 id="list-item-2">Item 2</h4>
                            <p>...</p>
                            <h4 id="list-item-3">Item 3</h4>
                            <p>...</p>
                            <h4 id="list-item-4">Item 4</h4>
                            <p>...</p>
                          </div>

## Usage

###### Via data attributes

To easily add scrollspy behavior to your topbar navigation, add `data-spy="scroll"` to the element you want to spy on (most typically this would be the `<body>`). Then add the `data-target` attribute with the ID or class of the parent element of any Bootstrap `.nav` component.

                    body {
                      position: relative;
                    }

                    <body data-spy="scroll" data-bs-target="#navbar-example">
                      ...
                      <div id="navbar-example">
                        <ul class="nav nav-tabs" role="tablist">
                          ...
                        </ul>
                      </div>
                      ...
                    </body>

###### Via JavaScript

After adding `position: relative;` in your CSS, call the scrollspy via JavaScript:

                    var scrollSpy = new bootstrap.ScrollSpy(document.body, {
                      target: '#navbar-example'
                    })

> ##### Resolvable ID targets required

> Navbar links must have resolvable id targets. For example, a `<a href="#home">home</a>` must correspond to something in the DOM like `<div id="home"></div>`.

##### Non-visible target elements ignored

Target elements that are not visible will be ignored and their corresponding nav items will never be highlighted.

## Methods

###### refresh

When using scrollspy in conjunction with adding or removing of elements from the DOM, you’ll need to call the refresh method like so:

                    var dataSpyList = [].slice.call(document.querySelectorAll('[data-spy="scroll"]'))
                    dataSpyList.forEach(function (dataSpyEl) {
                      bootstrap.ScrollSpy.getInstance(dataSpyEl)
                        .refresh()
                    })

###### dispose

Destroys an element’s scrollspy.

###### getInstance

Static method which allows you to get the scrollspy instance associated with a DOM element

                    var scrollSpyContentEl = document.getElementById('content')
                    var scrollSpy = bootstrap.ScrollSpy.getInstance(scrollSpyContentEl) // Returns a Bootstrap scrollspy instance

###### Options

Options can be passed via data attributes or JavaScript. For data attributes, append the option name to `data-`, as in `data-offset=""`.

Name | Type | Default | Description
--- | --- | --- | ---
offset | number | 10 | Pixels to offset from top when calculating position of scroll.
method | string | auto | Finds which section the spied element is in. `auto` will choose the best method to get scroll coordinates. `offset` will use the `Element.getBoundingClientRect()` method to get scroll coordinates. `position` will use the `HTMLElement.offsetTop` and `HTMLElement.offsetLeft` properties to get scroll coordinates.
target | string | jQuery object | DOM element |  | Specifies element to apply Scrollspy plugin.

###### Events

Event type | Description
--- | ---
activate.bs.scrollspy | This event fires on the scroll element whenever a new item becomes activated by the scrollspy.

                    var firstScrollSpyEl = document.querySelector('[data-spy="scroll"]')
                    firstScrollSpyEl.addEventListener('activate.bs.scrollspy', function () {
                      // do something...
                    })