Convert Utilities to TypeScript

frontend/src/Utilities/Array/getIndexOfFirstCharacter.js

@@ -1,11 +0,0 @@
-export default function getIndexOfFirstCharacter(items, character) {
-  return items.findIndex((item) => {
-    const firstCharacter = item.sortTitle.charAt(0);
-
-    if (character === '#') {
-      return !isNaN(firstCharacter);
-    }
-
-    return firstCharacter === character;
-  });
-}

frontend/src/Utilities/Array/getIndexOfFirstCharacter.ts

@@ -0,0 +1,18 @@
+import Series from 'Series/Series';
+
+const STARTS_WITH_NUMBER_REGEX = /^\d/;
+
+export default function getIndexOfFirstCharacter(
+  items: Series[],
+  character: string
+) {
+  return items.findIndex((item) => {
+    const firstCharacter = item.sortTitle.charAt(0);
+
+    if (character === '#') {
+      return STARTS_WITH_NUMBER_REGEX.test(firstCharacter);
+    }
+
+    return firstCharacter === character;
+  });
+}