Move image fetching out of LazyImage component into lib

src/lib/components/LazyImage.svelte

@@ -1,6 +1,7 @@
 <script lang="ts">
   import type { HTMLImgAttributes } from "svelte/elements";
   import { lazyload } from "$lib/lazyload";
+  import { fetch_image_base64 } from "$lib/image";
 
   interface LazyImageProps extends HTMLImgAttributes {
     /** The URL to the image resource to lazyload */
@@ -9,20 +10,6 @@
 
   let { src, ...restProps }: LazyImageProps = $props();
 
-  const blobToBase64 = (blob: Blob): Promise<any> => {
-    return new Promise((resolve, _) => {
-      const reader = new FileReader();
-      reader.onloadend = () => resolve(reader.result);
-      reader.readAsDataURL(blob);
-    });
-  };
-
-  const loadImage = async (url: string): Promise<any> => {
-    return await fetch(url)
-      .then((response) => response.blob())
-      .then((blob) => blobToBase64(blob));
-  };
-
   const lazy_visible_handler = () => {
     load = true;
   };
@@ -33,9 +20,7 @@
 
 <div use:lazyload onLazyVisible={lazy_visible_handler}>
   {#if load}
-    {#await loadImage(src)}
+    {#await fetch_image_base64(src) then data}
-      <!-- Loading... -->
-    {:then data}
       <img src={data} style="width: 100%" {...restProps} />
     {/await}
   {/if}

src/lib/image.ts

@@ -45,3 +45,22 @@ export const get_image_preview_event_handler = (id: string): ((event: Event) =>
 
   return handler;
 };
+
+/** Convert a binary [Blob] to base64 string */
+export const blob_to_base64 = (blob: Blob): Promise<string> => {
+  return new Promise((resolve, _) => {
+    const reader = new FileReader();
+
+    // This is fired once the file read has ended
+    reader.onloadend = () => resolve(reader.result?.toString() ?? "");
+
+    reader.readAsDataURL(blob);
+  });
+};
+
+/** Fetch an image from an URL using a fetch function [f] and return as base64 string */
+export const fetch_image_base64 = async (url: string, f: Function = fetch): Promise<string> => {
+  return f(url)
+    .then((response: Response) => response.blob())
+    .then((blob: Blob) => blob_to_base64(blob));
+};