<thumb-hash>

A custom element that automatically renders a thumbhash placeholder for your lazy-loaded images

Demo

thumbhash-custom-element.netlify.app

Scope & Motivation

This package is intended for frontend-only use only. It assumes you have already pre-generated your thumbhashes on the server or during an SSG build step. Many server-side libraries already provide convenience functions that will generate a thumbhash data URI for you. This is fine for pages with a few images, but will quickly increase the size of your html if you have more images. This is where thumbhash-custom-element comes in. All data-heavy calculation will be executed on the frontend, keeping your html small.

Installation

Install from npm and import it into your bundle:

npm i @hirasso/thumbhash-custom-element

import { ThumbHashElement } from "thumbhash-custom-element";
ThumbHashElement.init();

Or include the minified production file from a CDN:

<script type="module">
  import { ThumbHashElement } from "https://unpkg.com/@hirasso/thumbhash-custom-element@0?module";
  ThumbHashElement.init();
</script>

Usage

Markup

Add <thumb-hash> elements with your pre-generated thumbhash strings to your markup:

<figure>
+  <thumb-hash value="YTkGJwaRhWUIt4lbgnhZl3ath2BUBGYA" />
  <img src="https://example.com/image.jpg" loading="lazy" width="32" height="32" alt="My large lazy-loaded image">
</figure>

Result:

<figure>
+  <thumb-hash value="YTkGJwaRhWUIt4lbgnhZl3ath2BUBGYA" aria-hidden="true">
+    ⏷ #shadow-root (open)
+       <canvas width="32" height="32" style="width: 100%; height: 100%;"></canvas>
+  </thumb-hash>
  <img src="https://example.com/image.jpg" loading="lazy" width="32" height="32" alt="My large lazy-loaded image">
</figure>

Styling

figure,
figure img {
  position: relative;
}
thumb-hash {
  display: block;
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  object-fit: cover;
}

Strategies

The default strategy of <thumb-hash> is to render a canvas with the blurry representation of the thumbhash. Other options are img and average:

Strategy: img

Add the attribute strategy="img" to render an image with a data URI:

<figure>
+  <thumb-hash strategy="img" value="YTkGJwaRhWUIt4lbgnhZl3ath2BUBGYA" />
  <img src="https://example.com/image.jpg" loading="lazy" width="32" height="32" alt="My large lazy-loaded image">
</figure>

Result:

<figure>
+  <thumb-hash strategy="img" value="YTkGJwaRhWUIt4lbgnhZl3ath2BUBGYA" aria-hidden="true">
+    ⏷ #shadow-root (open)
+       <img alt="" src="data:image/png;base64,iVBORw0KGgo..." style="width: 100%; height: 100%;">
+  </thumb-hash>
  <img src="https://example.com/image.jpg" loading="lazy" width="32" height="32" alt="My large lazy-loaded image">
</figure>

Strategy: average

Add the attribute strategy="average" to render a div with the average color:

<figure>
+  <thumb-hash strategy="average" value="YTkGJwaRhWUIt4lbgnhZl3ath2BUBGYA" />
  <img src="https://example.com/image.jpg" loading="lazy" width="32" height="32" alt="My large lazy-loaded image">
</figure>

Result:

<figure>
+  <thumb-hash strategy="average" value="YTkGJwaRhWUIt4lbgnhZl3ath2BUBGYA" aria-hidden="true">
+    ⏷ #shadow-root (open)
+       <div style="width: 100%; height: 100%; background: rgb(111, 51, 0);"></div>
+  </thumb-hash>
  <img src="https://example.com/image.jpg" loading="lazy" width="32" height="32" alt="My large lazy-loaded image">
</figure>