added resize.js

app/static/resize.js

@@ -0,0 +1,34 @@
+async function resize(image_file,max_size=1000){
+    // Load the image
+    // Get as image data
+    const imageBitmap = await createImageBitmap(image_file);
+    
+    // Resize the image
+    var canvas = document.createElement('canvas'),
+    
+    width = imageBitmap.width,
+    height = imageBitmap.height;
+    if (width > height) {
+        if (width > max_size) {
+            height *= max_size / width;
+            width = max_size;
+        }
+    } else {
+        if (height > max_size) {
+            width *= max_size / height;
+            height = max_size;
+        }
+    }
+    canvas.width = width;
+    canvas.height = height;
+    canvas.getContext('2d').drawImage(imageBitmap, 0, 0, width, height);
+    
+    const blob = await new Promise((resolve) =>
+            canvas.toBlob(resolve, 'image/jpeg')
+        );
+
+    // Turn Blob into File
+    return new File([blob], image_file.name, {
+        type: blob.type,
+    });
+}