move json data fetching to a standalone module

assets/ts/dataFetch.ts

@@ -0,0 +1,19 @@
+interface ImageData {
+  index: string
+  url: string
+  imgH: string
+  imgW: string
+}
+
+// fetch images info from JSON
+const imageArrayElement = document.getElementById('images_array') as HTMLScriptElement
+const rawImageArray = imageArrayElement.textContent as string
+export const imagesArray: ImageData[] = JSON.parse(rawImageArray).sort(
+  (a: ImageData, b: ImageData) => {
+    if (a.index < b.index) {
+      return -1
+    }
+    return 1
+  }
+)
+export const imagesArrayLen: number = imagesArray.length