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amp-base-carousel

Experimental
Bento

Description

Displays multiple similar pieces of content along a horizontal axis or vertical axis.

 

Required Scripts

<script async custom-element="amp-base-carousel" src="https://cdn.ampproject.org/v0/amp-base-carousel-1.0.js"></script>

Usage

A generic carousel for displaying multiple similar pieces of content along a horizontal or vertical axis.

Each of the amp-base-carousel component’s immediate children is considered an item in the carousel. Each of these nodes may also have arbitrary HTML children.

The carousel consists of an arbitrary number of items, as well as optional navigational arrows to go forward or backwards a single item.

The carousel advances between items if the user swipes or uses the customizable arrow buttons.

Standalone use outside valid AMP documents

Bento AMP allows you to use AMP components in non-AMP pages without needing to commit to fully valid AMP. You can take these components and place them in implementations with frameworks and CMSs that don't support AMP. Read more in our guide Use AMP components in non-AMP pages.

Example

The example below demonstrates amp-base-carousel component in standalone use.

<head>
  <script async src="https://cdn.ampproject.org/v0.js"></script>
  <link rel="stylesheet" type="text/css" href="https://cdn.ampproject.org/v0/amp-base-carousel-1.0.css">
  <script async custom-element="amp-base-carousel" src="https://cdn.ampproject.org/v0/amp-base-carousel-1.0.js"></script>
  <style>
    amp-base-carousel, amp-base-carousel > div {
      aspect-ratio: 4/1;
    }
    .red-gradient {
      background: brown;
      background: linear-gradient(90deg, brown 50%, lightsalmon 90%, wheat 100%);
    }
    .blue-gradient {
      background: steelblue;
      background: linear-gradient(90deg, steelblue 50%, plum 90%, lavender 100%);
    }
    .green-gradient {
      background: seagreen;
      background: linear-gradient(90deg, seagreen 50%, mediumturquoise 90%, turquoise 100%);
    }
  </style>
</head>
<amp-base-carousel id="my-carousel">
  <div class="red-gradient"></div>
  <div class="blue-gradient"></div>
  <div class="green-gradient"></div>
</amp-base-carousel>
<div class="buttons" style="margin-top: 8px;">
  <button id='prev-button'>Go to previous slide</button>
  <button id='next-button'>Go to next slide</button>
  <button id='go-to-button'>Go to slide with green gradient</button>
</div>

<script>
  (async () => {
    const carousel = document.querySelector('#my-carousel');
    await customElements.whenDefined('amp-base-carousel');
    const api = await carousel.getApi();

    // programatically advance to next slide
    api.next();

    // set up button actions
    document.querySelector('#prev-button').onclick = () => api.prev();
    document.querySelector('#next-button').onclick = () => api.next();
    document.querySelector('#go-to-button').onclick = () => api.goToSlide(2);
  })();
</script>

Interactivity and API usage

Bento enabled components in standalone use are highly interactive through their API. In Bento standalone use, the element's API replaces AMP Actions and events and amp-bind.

The amp-base-carousel component API is accessible by including the following script tag in your document:

await customElements.whenDefined('amp-base-carousel');
const api = await carousel.getApi();
Actions

The amp-base-carousel API allows you to perform the following actions:

next() Moves the carousel forwards by advance-count slides.

api.next();

prev() Moves the carousel backwards by advance-count slides.

api.prev();

goToSlide(index: number) Moves the carousel to the slide specified by the index argument.

index will be normalized to a number greater than or equal to 0 and less than the number of slides given.

api.goToSlide(0); // Advance to first slide.
api.goToSlide(length - 1); // Advance to last slide.
Events

The amp-base-carousel API allows you to register and respond to the following events:

slideChange

This event is triggered when the index displayed by the carousel has changed. The new index is available via event.data.index.

carousel.addEventListener('slideChange', (e) => console.log(e.data.index))

Layout and style

Each Bento component has a small CSS library you must include to guarantee proper loading without content shifts. Because of order-based specificity, you must manually ensure that stylesheets are included before any custom styles.

<link rel="stylesheet" type="text/css" href="https://cdn.ampproject.org/v0/amp-base-carousel-1.0.css">

Fully valid AMP pages use the AMP layout system to infer sizing of elements to create a page structure before downloading any remote resources. However, Bento use imports components into less controlled environments and AMP's layout system is inaccessible.

Container type

The amp-base-carousel component has a defined layout size type. To ensure the component renders correctly, be sure to apply a size to the component and its immediate children (slides) via a desired CSS layout (such as one defined with height, width, aspect-ratio, or other such properties):

amp-base-carousel {
  height: 100px;
  width: 100%;
}

amp-base-carousel > * {
  aspect-ratio: 4/1
}

Behavior users should be aware of

RTL

<amp-base-carousel> currently requires that you let it know when it is in an right-to-left (rtl) context (e.g. Arabic, Hebrew pages). While the carousel will generally work without this, there may be a few bugs. You can let the carousel know that it should operate as rtl as follows:

<amp-base-carousel dir="rtl" ></amp-base-carousel>

If the carousel is in a RTL context, and you want the carousel to operate as LTR, you can explicitly set the dir="ltr" on the carousel.

Slide layout

Slides are automatically sized by the carousel when not specifying mixed-lengths. You should give the slides layout="flex-item":

<amp-base-carousel >
  <amp-img layout="flex-item" src="…"></amp-img>
</amp-base-carousel>

The slides have a default height of 100% when the carousel is laid out horizontally. This can easily be changed with CSS or by using layout="fixed-height". When specifying the height, the slide will be vertically centered within the carousel.

If you want to horizontally center your slide content, you will want to create a wrapping element, and use that to center the content.

Number of Visible Slides

When changing the number of visible slides using visible-slides, in response to a media query, you will likely want to change the aspect ratio of the carousel itself to match the new number of visible slides. For example, if you want to show three slides at a time with a one by one aspect ratio, you would want an aspect ratio of three by one for the carousel itself. Similiarly, with four slides at a time you would want an aspect ratio of four by one. In addition, when changing visible-slides, you likely want to change advance-count.

<!-- Using an aspect ratio of 3:2 for the slides in this example. -->
<amp-base-carousel
  layout="responsive"
  width="3"
  height="1"
  heights="(min-width: 600px) calc(100% * 4 * 3 / 2), calc(100% * 3 * 3 / 2)"
  visible-count="(min-width: 600px) 4, 3"
  advance-count="(min-width: 600px) 4, 3"
>
  <amp-img layout="flex-item" src="…"></amp-img></amp-base-carousel>

Attributes

Media Queries

The attributes for <amp-base-carousel> can be configured to use different options based on a media query.

Configuration Options

Number of Visible Slides

mixed-length

Either true or false, defaults to false. When true, uses the existing width (or height when horizontal) for each of the slides. This allows for a carousel with slides of different widths to be used.

visible-count

A number, defaults to 1. Determines how many slides should be shown at a given time. Fractional values can be used to make part of a(n) additional slide(s) visible. This option is ignored when mixed-length is true.

advance-count

A number, defaults to 1. Determines how many slides the carousel will advance when advancing using the previous or next arrows. This is useful when specifying the visible-count attribute.

Auto Advance

auto-advance

Either true or false, defaults to false. Automatically advances the carousel to the next slide based on a delay. If the user manually changes slides, then the auto advance is stopped. Note that if loop is not enabled, when reaching the last item, the auto advance will move backwards to the first item.

auto-advance-count

A number, defaults to 1. Determines how many slides the carousel will advance when automatically advancing. This is useful when specifying the visible-count attribute.

auto-advance-interval

A number, defaults to 1000. Specifies the amount of time, in milliseconds, between subsequent automatic advances of the carousel.

auto-advance-loops

A number, defaults to . The number of times the carousel should advance through the slides before stopping.

Snapping

snap

Either true or false, defaults to true. Determines whether or not the carousel should snap on slides when scrolling.

snap-align

Either start or center. When start aligning, the start of a slide (e.g. the left edge, when horizontal aligning) is aligned with the start of a carousel. When center aligning, the center of a slide is aligned with the center of a carousel.

snap-by

A number, defaults to 1. This determines the granularity of snapping and is useful when using visible-count.

Miscellaneous

controls

Either "always", "auto", or "never", defaults to "auto". This determines if and when prev/next navigational arrows are displayed. Note: When outset-arrows is true, the arrows are shown "always".

  • always: Arrows are always displayed.
  • auto: Arrows are displayed when the carousel has most recently received interaction via mouse, and not displayed when the carousel has most recently received interaction via touch. On first load for touch devices, arrows are displayed until first interaction.
  • never: Arrows are never displayed.
slide

A number, defaults to 0. This determines the initial slide shown in the carousel. This may be used with amp-bind to control which slide is currently showing.

loop

Either true or false, defaults to false when omitted. When true, the carousel will allow the user to move from the first item back to the last item and visa versa. There must be at least three times the visible-count of slides present for looping to occur.

orientation

Either horizontal or vertical, defaults to horizontal. When horizontal the carousel will lay out horizontally, with the user being able to swipe left and right. When vertical, the carousel lays out vertically, with the user being able to swipe up and down.

common attributes

This element includes common attributes extended to AMP components.

Actions

next

Moves the carousel forwards by advance-count slides.

prev

Moves the carousel backwards by advance-count slides.

goToSlide

Moves the carousel to the slide specified by the index argument.

Events

slideChange

This event is triggered when the index displayed by the carousel has changed. The new index is available via event.index.

Styling

You may use the amp-base-carousel element selector to style the carousel freely.

Customizing Arrow Buttons

Arrow buttons can be customized by passing in your own custom markup. For example, you can recreate the default styling with the following HTML and CSS:

.carousel-prev,
.carousel-next {
  filter: drop-shadow(0px 1px 2px #4a4a4a);
  width: 40px;
  height: 40px;
  padding: 20px;
  background-color: transparent;
  border: none;
  outline: none;
}

.carousel-prev {
  background-image: url('data:image/svg+xml;charset=utf-8,<svg viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path  d="M14,7.4 L9.4,12 L14,16.6" fill="none" stroke="#fff" stroke-width="2px" stroke-linejoin="round" stroke-linecap="round" /></svg>');
}

.carousel-next {
  background-image: url('data:image/svg+xml;charset=utf-8,<svg viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path  d="M10,7.4 L14.6,12 L10,16.6" fill="none" stroke="#fff" stroke-width="2px" stroke-linejoin="round" stroke-linecap="round" /></svg>');
}
<amp-base-carousel >
  <div>first slide</div><button slot="next-arrow" class="carousel-next" aria-label="Next"></button>
  <button
    slot="prev-arrow"
    class="carousel-prev"
    aria-label="Previous"
  ></button>
</amp-base-carousel>

If you want more customization for the arrow buttons, you can use the next and prev actions. For example, if you want to place buttons under the carousel and use the words "Previous" and "Next" instead of having them in the default location, you can use the following HTML:

  <amp-base-carousel id="carousel-1" ><div slot="next-arrow"></div>
    <div slot="prev-arrow"></div>
  </amp-carousel>
  <button on="tap:carousel-1.prev()">Previous</button>
  <button on="tap:carousel-1.next()">Next</button>

Version notes

Unlike 0.1, the experimental 1.0 version of amp-base-carousel allows configuring the carousel slide orientation via "orientation"="horizontal"|"vertical" attributes instead of "horizontal"="true"|"false" attributes.

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