Gumshoe
A simple vanilla JS scrollspy script. Gumshoe works great with Smooth Scroll.
View the Demo on CodePen →
Getting Started | Nested Navigation | Reflows | Fixed Headers | API | What's new? | Browser Compatibility | License
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Getting Started
Compiled and production-ready code can be found in the dist
directory. The src
directory contains development code.
1. Include Gumshoe on your site.
There are two versions of Gumshoe: the standalone version, and one that comes preloaded with polyfills for closest()
and CustomEvent()
, which are only supported in newer browsers.
If you're including your own polyfills or don't want to enable this feature for older browsers, use the standalone version. Otherwise, use the version with polyfills.
Direct Download
You can download the files directly from GitHub.
<script src="path/to/gumshoe.polyfills.min.js"></script>
CDN
You can also use the jsDelivr CDN. I recommend linking to a specific version number or version range to prevent major updates from breaking your site. Gumshoe uses semantic versioning.
<script src="https://cdn.jsdelivr.net/gh/cferdinandi/gumshoe/dist/gumshoe.polyfills.min.js"></script>
<script src="https://cdn.jsdelivr.net/gh/cferdinandi/gumshoe@4/dist/gumshoe.polyfills.min.js"></script>
<script src="https://cdn.jsdelivr.net/gh/cferdinandi/gumshoe@4.0/dist/gumshoe.polyfills.min.js"></script>
<script src="https://cdn.jsdelivr.net/gh/cferdinandi/gumshoe@4.0.0/dist/gumshoe.polyfills.min.js"></script>
NPM
You can also use NPM (or your favorite package manager).
npm install gumshoejs
2. Add the markup to your HTML.
The only thing Gumshoe needs to work is a list of anchor links. They can be ordered or unordered, inline or unstyled, or even nested.
<ul id="my-awesome-nav">
<li><a href="#eenie">Eenie</a></li>
<li><a href="#meenie">Meenie</a></li>
<li><a href="#miney">Miney</a></li>
<li><a href="#mo">Mo</a></li>
</ul>
3. Initialize Gumshoe.
In the footer of your page, after the content, initialize Gumshoe by passing in a selector for the navigation links that should be detected as the user scrolls.
<script>
var spy = new Gumshoe('#my-awesome-nav a');
</script>
4. Add styling.
Gumshoe adds the .active
class to the list item (<li></li>
) and content for the active link, but does not include any styling.
Add styles to your CSS as desired. And that's it, you're done. Nice work!
#my-awesome-nav li.active a {
font-weight: bold;
}
View a Demo on CodePen →
Note: you can customize the class names with user options.
Nested navigation
If you have a nested navigation menu with multiple levels, Gumshoe can also apply an .active
class to the parent list items of the currently active link.
<ul id="my-awesome-nav">
<li><a href="#eenie">Eenie</a></li>
<li>
<a href="#meenie">Meenie</a>
<ul>
<li><a href="#hickory">Hickory</a></li>
<li><a href="#dickory">Dickory</a></li>
<li><a href="#doc">Doc</a></li>
</ul>
</li>
<li><a href="#miney">Miney</a></li>
<li><a href="#mo">Mo</a></li>
</ul>
Set nested
to true
when instantiating Gumshoe. You can also customize the class name.
var spy = new Gumshoe('#my-awesome-nav a', {
nested: true,
nestedClass: 'active-parent'
});
Try nested navigation on CodePen →
Catching reflows
If the content that's linked to by your navigation has different layouts at different viewports, Gumshoe will need to detect these changes and update some calculations behind-the-scenes.
Set reflow
to true
to enable this (it's off by default).
var spy = new Gumshoe('#my-awesome-nav a', {
reflow: true
});
If you have a fixed header on your page, you may want to offset when a piece of content is considered "active."
The offset
user setting accepts either a number, or a function that returns a number. If you need to dynamically calculate dimensions, a function is the preferred method.
Here's an example that automatically calculates a header's height and offsets by that amount.
var header = document.querySelector('#my-header');
var spy = new Gumshoe('#my-awesome-nav a', {
offset: function () {
return header.getBoundingClientRect().height;
}
});
Try using an offset on CodePen →
API
Gumshoe includes smart defaults and works right out of the box. But if you want to customize things, it also has a robust API that provides multiple ways for you to adjust the default options and settings.
Options and Settings
You can pass options into Gumshoe when instantiating.
var spy = new Gumshoe('#my-awesome-nav a', {
navClass: 'active',
contentClass: 'active',
nested: false,
nestedClass: 'active',
offset: 0,
reflow: false,
events: true
});
Custom Events
Gumshoe emits two custom events:
gumshoeActivate
is emitted when a link is activated.gumshoeDeactivate
is emitted when a link is deactivated.
Both events are emitted on the list item and bubble up. You can listen for them with the addEventListener()
method. The event.detail
object includes the link
and content
elements, and the settings
for the current instantiation.
document.addEventListener('gumshoeActivate', function (event) {
var li = event.target;
var link = event.detail.link;
var content = event.detail.content;
}, false);
Methods
Gumshoe also exposes several public methods.
setup()
Setups all of the calculations Gumshoe needs behind-the-scenes. If you dynamically add navigation items to the DOM after Gumshoe is instantiated, you can run this method to update the calculations.
Example
var spy = new Gumshoe('#my-awesome-nav a');
spy.setup();
detect()
Activate the navigation link that's content is currently in the viewport.
Example
var spy = new Gumshoe('#my-awesome-nav a');
spy.detect();
destroy()
Destroy the current instantiation of Gumshoe.
Example
var spy = new Gumshoe('#my-awesome-nav a');
spy.destroy();
What's new?
Gumshoe 4 is a ground-up rewrite.
New Features
- Multiple instantiations can be run with different settings for each.
- An active class is now added to the content as well.
- Nested navigation is now supported.
- Offsets can be dynamically calculated instead of set just once at initialization.
- Special and non-Roman characters can now be used in anchor links and IDs.
- Custom events provide a more flexible way to react to DOM changes.
Breaking Changes
- Gumshoe must now be instantiated as a new object (
new Gumshoe()
) instead of being initialized gumshoe.init()
. - Callback methods have been removed in favor of events.
- Automatic header offsetting has been removed.
- The public
init()
method has been deprecated.
Browser Compatibility
Gumshoe works in all modern browsers, and IE 9 and above.
Polyfills
Support back to IE9 requires polyfills for closest()
and CustomEvent()
. Without them, support starts with Edge.
Use the included polyfills version of Gumshoe, or include your own.
License
The code is available under the MIT License.