Extract max file size so it can be computed later.

src/common-components/textbox-question/textbox-question.vue

@@ -159,9 +159,8 @@ export default {
         },
 
         isImageValid(imageFile) {
-            let maxSize = 0.5 * 1028 * 1028;
 
-            return imageFile && imageFile.size < maxSize;
+            return imageFile && imageFile.size < this.maxFileSize;
         },
     },
     computed: {
@@ -200,6 +199,12 @@ export default {
                 return questionText;
             },
         },
+
+        maxFileSize() {
+            let kiloBytes = 512;
+
+            return kiloBytes * 1028;
+        }
     },
     watch: {
         async value(newValue) {