Scroll to top
Introduction
amp-position-observer combined with amp-animation can be used to implement a scroll to top button. This pattern is often used in e-commerce pages where the user has to scroll through a long list of items.
Setup
Import amp-position-observer extension
<script async custom-element="amp-position-observer" src="https://cdn.ampproject.org/v0/amp-position-observer-0.1.js"></script>
Import amp-animation extension
<script async custom-element="amp-animation" src="https://cdn.ampproject.org/v0/amp-animation-0.1.js"></script>
Styles
The CSS used for these samples are included here for reference.
These rules are simply needed to make the samples work but are not fundamental to the concepts covered here.
<style amp-custom>
:root {
--color-primary: #005AF0;
--color-secondary: #00DCC0;
--color-text-light: #fff;
--space-2: 1rem; /* 16px */
--box-shadow-1: 0 1px 1px 0 rgba(0,0,0,.14), 0 1px 1px -1px rgba(0,0,0,.14), 0 1px 5px 0 rgba(0,0,0,.12);
}
.scrollToTop {
color: var(--color-text-light);
font-size: 1.4em;
box-shadow: var(--box-shadow-1);
width: 50px;
height: 50px;
border-radius: 50%;
border: none;
outline: none;
background: var(--color-primary);
z-index: 9999;
bottom: var(--space-2);
right: var(--space-2);
position: fixed;
opacity: 0;
visibility: hidden;
}
.spacer {
width: 100vw;
max-width: 700px;
height: 200vh;
background-color: var(--color-secondary);
}
/* we move the anchor down to componsate the fixed header */
.target {
position: relative;
}
.target-anchor {
position: absolute;
top: -72px;
left: 0;
}
</style>
Position observer and animation
We add an element with id top-page
that we can reference later for scrolling. We use amp-position-observer
to start the animation when the user starts to scroll and the element at the top is no longer visible.
<h3 class="target">
<a class="target-anchor" id="top"></a>
This is the target.
<amp-position-observer on="enter:hideAnim.start; exit:showAnim.start" layout="nodisplay">
</amp-position-observer>
</h3>
We use 2 amp-animation
elements to trigger the visibility of the button. The first one is for making the button visible...
<amp-animation id="showAnim" layout="nodisplay">
<script type="application/json">
{
"duration": "200ms",
"fill": "both",
"iterations": "1",
"direction": "alternate",
"animations": [
{
"selector": "#scrollToTopButton",
"keyframes": [
{ "opacity": "1", "visibility": "visible" }
]
}
]
}
</script>
</amp-animation>
... and the second one is for adding the button.
<amp-animation id="hideAnim" layout="nodisplay">
<script type="application/json">
{
"duration": "200ms",
"fill": "both",
"iterations": "1",
"direction": "alternate",
"animations": [
{
"selector": "#scrollToTopButton",
"keyframes": [
{ "opacity": "0", "visibility": "hidden" }
]
}
]
}
</script>
</amp-animation>
Here is a dummy spacer.
<div class="spacer"></div>
The scroll to top button
We use the scrollTo
action to scroll the page when the button is tapped. Find more about actions here.
<button id="scrollToTopButton" on="tap:top.scrollTo(duration=200)" class="scrollToTop">⌃</button>
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Written by @kul3r4