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Lazuli/src/lib/components/media/lazyImage.svelte

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<!--
@component
A component to help render images in a smooth and efficient way. The url passed will be fetched via Lazuli's
remoteImage API endpoint with size parameters that are dynamically calculated base off of the image's container's
width and height. Images are lazily loaded unless 'eager' loading is specified.
@param thumbnailUrl A string of a URL that points to the desired image.
@param alt Supplementary text in the event the image fails to load.
@param loadingMethod Optional. Either the string 'lazy' or 'eager', defaults to lazy. The method by which to load the image.
-->
<script lang="ts">
import { onMount } from 'svelte'
export let thumbnailUrl: string
export let alt: string
export let loadingMethod: 'lazy' | 'eager' = 'lazy'
let imageContainer: HTMLDivElement
function removeOldImage() {
if (imageContainer.childElementCount > 1) {
const oldImage = imageContainer.firstChild! as HTMLImageElement
oldImage.style.opacity = '0'
setTimeout(() => imageContainer.removeChild(oldImage), 500)
}
}
function updateImage(newThumbnailURL: string) {
if (!imageContainer) return
const width = imageContainer.clientWidth
const height = imageContainer.clientHeight
const newImage = new Image(width, height)
imageContainer.appendChild(newImage)
newImage.loading = loadingMethod
newImage.src = `/api/remoteImage?url=${newThumbnailURL}&`.concat(width > height ? `maxWidth=${width}` : `maxHeight=${height}`)
newImage.alt = alt
newImage.style.width = '100%'
newImage.style.height = '100%'
newImage.style.objectFit = 'cover'
newImage.style.opacity = '0'
newImage.style.position = 'absolute'
newImage.onload = () => {
removeOldImage()
newImage.style.transition = 'opacity 500ms ease'
newImage.style.opacity = '1'
}
newImage.onerror = () => {
removeOldImage()
newImage.style.opacity = '1'
}
}
onMount(() => updateImage(thumbnailUrl))
$: updateImage(thumbnailUrl)
</script>
<div bind:this={imageContainer} class="relative h-full w-full"></div>