some basic viewer

script/download.ts

@@ -0,0 +1,28 @@
+export async function download(url: string, progress: (number) => void): Promise<ArrayBuffer> {
+    const response = await fetch(url, {mode: 'cors'});
+
+    if (!response.body || !response.headers) {
+        throw new Error("invalid response");
+    }
+    const contentLength = +(response.headers.get('Content-Length') || 0);
+    let receivedLength = 0;
+
+    let data = new Uint8Array(contentLength);
+
+    const reader = response.body.getReader();
+
+    while(true) {
+        const {done, value} = await reader.read();
+
+        if (done) {
+            break;
+        }
+
+        data.set(value, receivedLength);
+        receivedLength += value.length;
+
+        progress((receivedLength / contentLength) * 100);
+    }
+
+    return data.buffer;
+}